Copyright 0 1991 by the Genetics Society of America
Perspectives
Anecdotal, Historical and Critical Commentaries on Genetics
Edited by James F. Crow and William F. Dove
The Regulationof Arginine Biosynthesis: Its Contributionto
Understanding the Controlof Gene Expression
Werner K. Maas
Department of Microbiology, New York University Medical Center, 550 First Avenue, New York, New York 10016
N the 1950s there occurred a fundamental change
in the outlook of biologists on the regulation of
biochemical processes. Certain studies on the regulation of arginine synthesis in Escherichia coli played a
role in bringing about this change and the present
article is an account of these studies. Because I started
to work on the regulation of arginine biosynthesis in
the mid-I950s, the story told here will be of a somewhat personal nature.
What was the nature of the fundamental change
that occurred in the 195Os?To answer this question I
shall first describe the general picture of the regulation of biochemical pathways and of gene expression
that was in vogue before the change. Regulation of
biochemical pathways belonged at that time in the
domain of biochemists, whereas regulation of gene
expression belonged in the domain of geneticists, and
there was little interchange of ideas between the two.
Inregardto
biochemical pathways, regulation was
thought to be somehow built into the chemical structures of enzymes and their substrates and products.
Rates of reactions were thought to be controlled by
affinities of substrates for their enzymes and by inhibition by products formed during a reaction. These
conceptsseemed to be implicit in the thinking of
biochemists and very little was said explicitly about
regulation in textbooks published at that time, such
as in the excellent book by FRUTONand SIMMONDS
(1 953).
In regard to the control
of gene expression, the
thinking of geneticists was very much influenced by
the one gene, oneenzyme hypothesis of BEADLE
and
TATUM,
which in a general form stated that a gene
determinesa specific protein molecule. Little was
known about how a gene determines a protein molecule and even less about how this gene activity was
I
This article is dedicated to the memory
of LEOSZILARD.
Genetics 128: 489-494 (July, 1991)
controlled. Again, this lackof concrete ideas was
reflected in then current textbooks of genetics. An
exception to the lack of specific information was the
work on adaptive enzymes, which at that time was
carried out mainly by JACQUES MONOD and his coworkers at the Pasteur Institute in Paris. It was shown
that for these enzymes, such as &galactosidase, the
substrate or an analog of the substrate was required
to bring about synthesis of the enzyme and that this
“induction” was controlled by a specific gene. Constitutive mutants were isolated in which the “inducer”
was no longer required for enzyme synthesis. MONOD’sinterpretation of the findings was that the inducer
somehow molded the informationintoan
enzymeforming system to produce a specific enzyme. In a
constitutive mutant, a specific gene gave rise to an
internal inducer, whereas in the wild type, this gene
was inactive and the inducer had to
be supplied externally. This picture of gene control, like that of the
control of enzymatic reactions, involves chemical information contained in the substrate, which brings
about regulation of, in one case, enzymatic reactions
and, in the other case, the synthesis of enzymes. The
thinking behind these concepts was based largely on
then current concepts of interactions between proteins and low molecular substrates and also on template mechanisms, such as that invoked for the synthesis of antibodies. The latter was developed largely
by HAUROWITZ
(1 952) and has been referred toas the
or “directtemplate”theory
HAUROWITZ-PAULING
(BURNET 1959). holds
It
that antibody molecules have
their specificity determined by being synthesized
against atemplate of theantigen molecules themselves.
The big change in thinking about regulation was
the realization that there is no direct chemical relationshipbetween the regulating substance and the
490
W. K. Maas
protein whose production is regulated by this substance. Instead, the response to the regulating substance is mediated by the products of genes whose
only function is the regulation of gene expression.
This view was expressed by LEDERBERG
(1 956) during
the discussion of a lecture by MONOD(1 956)in which
the latter had stated that“the ‘S’ substance (a common
precursor) might be capable of giving rise to several
different enzymes, depending on the nature
of the
inducer with which it reacted.”
LEDERBERG’S
response
phosphate
was, “Dr. MONOD asked whether the inducer carries
the information needed for the specification of the
enzyme. One permissible view holds that the enzyme,
or its critical surface, is directly molded on the inducing substrate. The alternative, which I prefer, is that
all the specifications are already inherent in the genetic constitution of the cell. The inducer signals a
regulatory system to accelerate the synthesis of the
corresponding enzyme protein.” This notion of specific regulatory gene products (presumably proteins)
was novel to biochemists and had a profound effect
on subsequent research in biochemistry. It brought
biochemists together with geneticists and it did much
to createthe field of molecular biology, inwhich
guidance was provided mainly bythe results of genetic
experiments. I have tried to formulate this change in
an article written for a Lipmann
Symposium (MAAS
1974) by saying, “It has become clearthat during
evolution, mechanisms previously considered
unlikely, can become established in living cells, as long
as they give the organism a selective advantage over
its competitors. The cell is no longer considered as a
chemical machine, but as a cybernetic chemical machine.”
The source of these novel ideas was the discovery
of end-product repression in biosynthetic pathways,
including that of arginine. These end productscould
control thesynthesis of enzymes whose substrates bore
little structural similarity to the end product.
Discovery of the repression of arginine biosynthesis: T o make it easier for the reader to follow the
text, the pathway of arginine biosynthesis in E . coli is
shown in Figure 1. T h e first studies were carried out
by HENRY
VOGEL(1953). He noticed that in an arginine-requiring mutant blocked before N-acetylornithine (Figure l), the level of acetylornithinase (Figure
1, step 5) was higher in cells grown with acetylornithinethan incells grown with arginine. He subsequently extended these studies by growing the cells
on mixed supplements of arginineand acetylornithine, in order to distinguish between induction by
acetylornithine or inhibition by arginine as an explanation for his observations. In 1957, in a paper given
at the McCollum Pratt Symposium (VOGEL1957), he
presented data showing that his observed effects were
due to inhibition by arginine. He coined theterm
1
Glutamate -N-acetylglutamate
2
4N-acetyl lutamyl
phoshate
\“I
N-acetylglutamlc
semialdehyde
1.
Arginine
7
Arglnlno +Citrulline
succinate
0
A A
+
Ornithine + Carbamyl
t9
ATP + Glutamine + CO2
FIGURE 1.-The
biosynthesis of arginine. T h e reactionsteps
shown arecontrolled by theargininerepressor.
T h e enzymes
catalyzing these reactions are,in order of the steps: 1, N-acetylglutamate synthase; 2, N-acetylglutamate kinase; 3, N-acetylglutamylphosphate reductase; 4,N-acetylornithine transaminase; 5 , N-acetyl
ornithinase; 6, ornithine carbamoyl transferase; 7, argininosuccinate synthetase;8, argininosuccinase; 9, carbamoylphosphate synthetase.
“enzymerepression” to describe this phenomenon.
The substance inhibitingenzyme synthesis was named
a “represser.”(The alternative spelling “repressor”has
since been accepted, whereas “promotor” has not.)
My own involvement with the regulation of arginine
biosynthesis began in 1955 and was unrelated to VOGEL’S work. At that time I was interested in how genes
control theproduction of enzymes. In 1952 I had
shown that in a temperature-sensitive mutant of E .
coli blocked in the synthesis of pantothenic acid, the
enzyme catalyzing the conditionally blocked reaction
was more heat-labile than the corresponding enzyme
in the wild type (MAASand DAVIS1952). The results
showed that an altered protein was produced as a
result of mutation and that a gene could therefore
control the structure of its protein product.
After a stay in LIPMANN’S laboratory
in 1953 and
1954, I returned to New York University to continue
the study of gene-enzyme relationships. I looked for
mutants of a known gene in which the rate of enzyme
synthesis was altered. T o d othis, I screened revertants
from completely blocked mutantsthat could grow
without the required growth factor at 37” but could
not at 25 (cold-sensitive mutants). One of the strains
from which I obtained such mutants was an arginine
auxotroph blocked between ornithine and citrulline
(Figure 1,step 6) and unable to make the enzyme
ornithine transcarbamoyltransferase (OTCase). From
this strain the desiredrevertants
were obtained.
OTCase was produced when the cells were grown at
37” but not at 25”.
At 25” the mutant had to
be
grown with arginine, but at 37” it grew in a minimal
medium without arginine. The surprise came when
the cells were grown at 37 ” with arginine: no OTCase
was produced.Subsequently, inhibition of OTCase
formation by arginine was found in the wild-type
O
Perspectives
strain as well, at both 37” and 25”. Itwas shown that
the inhibition was specific for arginine. Growth with
citrulline did not inhibit OTCase synthesis, whereas
growth with arginine did (MAAS 1956). Presumable
citrulline is converted to arginine too slowly to establish thearginineconcentrationrequiredfor
full
repression. In this roundabout way I had serendipitously discovered thatend-productrepression
of
OTCase was a general phenomenon and had nothing
to dowith the cold-sensitive mutations.
By 1957 it was thus established that arginine could
repress the formation of at least two enzymes in its
biosynthetic pathway. Both enzymes catalyzed reactions before the last step in the pathway. It seemed
most probablethat this repression was not due to
arginine alone and that other
components must be
involved. The most obvious way to look for such
components was to isolate mutants in which OTCase
formation was not repressed by arginine. I shall describe such mutants after first considering theimpact
of the argininestudies on the then current
ideas about
the regulation of enzyme formation.
A unified hypothesis for the regulationof enzyme
synthesis: In 1957, enzyme induction and enzyme
repression were two different ways in which the formation of an enzyme could be controlled.
At that time
the notion was prevalent that theprimary mechanism
for the two types of control should be thesame. This
view was especially propounded by MONOD.It is curious today to see this insistence on a unitary mechanism. The reason may be that, at thetime, our thinking was muchinfluenced by thethen fashionable
concept of the “Unity of Biochemistry.” I stated this
view during the discussion of a paper I presented in
1957 (MAAS and GORINI1958): “I think that most
people feel the distinction between adaptive (ie., inducible) and constitutive (it?.,biosynthetic) enzymes is
an artificial one. In the case of constitutive enzymes
the inducer is always present, whereas in the case of
adaptive enzymes it is ordinarily not present. Alternatively, it is possible that adaptive enzyme formation
is due to the inhibition of a feed-back inhibitor normally present, and thatinducers actby preventing the
action of such feed-back inhibitors.”
On the basis of his studies on the induction of pgalactosidase, MONOD at first believed strongly in induction as the primary mechanism (positive and “instructive” control). The story of how he changed his
mind and how the work on arginine regulation contributed to his conversion to a hypothesis involving
negative control has been told several times UIJDSON
1970; SCHAFFNER
1974; BROCK1990). Nevertheless,
I shall give my personal account of this history and of
the seminal role played byLEO SZILARDin the exchange of ideas.
I had already demonstrated (MAAS 1956) that the
49 1
substrate ornithine was not required for the synthesis
of OTCase and concluded, “here the substrate may
not function as an inducer forenzyme formation.” At
that time LUIGIGORINI,who was a visiting investigator
in our pharmacology department at New York University, joined me in investigating the kinetics of
OTCase formation. Following a discussion with NOVICK and SZILARD,
we decided to study OTCase synthesis in a chemostat, a device for constant growth
devised by NOVICKand SZILARD (1 950). our
For studies we used a mutant blocked before ornithine andwe
grew it in achemostat with arginine limiting the
growthrate.Under
theseconditionsOTCase
was
produced at a high “derepressed” rate,
yet its substrate
ornithine was not present in the bacteria (GORINIand
MAAS 1957).
In April, 1957 I attended the Federation Meetings
in Chicago and stayed at the Quadrangle Club where
SZILARD
was also staying. I met him during breakfast
and told him about the synthesis of OTCase in the
absence of a substrate. Yet the kinetics of enzyme
synthesis were like those observed during the induction of p-galactosidase. Onthe basisof aunitary
hypothesis, one had to conclude that induction was a
removal of repression andthattheinducer
acted
secondarily in counteracting a repressor. SZILARD
was
impressed with this idea and said that it could explain
some findings on P-galactosidase formation that MILTON WEINERhad made in their laboratory. We had
more discussions during breakfast on subsequent days
and at the endSZILARD
was ready to publish a paper.
I felt reluctant because we had no experimental evidence in an inducible system but SZILARD
did publish
a theoretical paper (SZILARD 1960).
Early in 1958, SZILARD presented the unitary hypothesis we had formulated in Chicago at a seminar
at thePasteur Institutein Paris. At that time, ARTHUR
PARDEE
in MONOD’Slaboratory hadjust begun to carry
out experiments tostudy the expression of the inducibility genefor @-galactosidaseformation following
transfer of this gene during matings (later known as
the PARDEE-JACOB-MONOD
or “Pajamo”experiment
or, in a lighter vein, the “Pajama” experiment). The
thinking of MONOD at that time was still in favor of
an “internal inducer” hypothesis but it appears that
SZILARD’S
seminar and the subsequent discussion had
a strong influence in convincing him of the validity of
the “removal of repressor” hypothesis to explain pgalactosidase induction. T o quote from MONOD’SNobel lecture, “Why not suppose, then, since the existence of repressible systems and their extreme generality were now proven, that induction could be effected by an anti-repressor, rather than repression by
an anti-inducer? This is precisely the thesis that LEO
SZILARD,while passing through Paris, happened to
propose to us during a seminar. We had only recently
492
W. K. Maas
obtained the first results of the injection (‘Pajama’)
experiment, andwe were still not sure aboutits interpretation. I saw thatour preliminaryobservations
confirmed SZILARD’S
penetrating intuition, and when
he had finished his presentation, my doubts about the
theory of the ‘double bluff‘ (inductionequals removal
of repression) had been removed. . .” (MONOD1966).
T h e results of the completed experimentsdid indeed
establish the validity of the “removal of repressor”
model as originally postulated from results with the
repression of OTCase. It is interesting that the belief
in a unitary mechanism had such a strong influence
on the willingness of MONODand others toaccept the
interpretation of theinducer as an anti-repressor.
Nowadays, and for goodreasons, our attitude has
become muchmore flexible because bothprimary
negative actions and primary positive actionshave
been found in the control of enzyme synthesis.
Isolation and properties of derepressed (argR-)
mutants: In order to study components other than
arginine required for repression,I started to look for
derepressed mutants in 1957. Canavanine, an analog
of arginine,was found toinhibit growth by competing
for arginine in protein synthesis (SCHWARTZ
and MAAS
1960). It seemed reasonable to suppose that mutants
resistant to canavanine might be derepressedbecause
they would produce more arginine than the repressible wild type and thus overcome inhibition by canavanine.
At that time our wild-type strain was E. coli W. We
isolated many canavanine-resistant mutants but they
all turned out to be defective in the uptake of canavanine,
arginine
and
other
basic amino acids
MAAS and SIMON 1959). These mutants
(SCHWARTZ,
started us on further investigations of permeases for
basic amino acids.
During the summer of 1959 1 worked in JACOB’S
laboratory at the Pasteur Institute in Paris and again
I looked for canavanine-resistant mutants, this time
starting with E. coli K12. The first mutants I isolated
were derepressed for OTCase.Later they were shown
to be derepressed also for other enzymes of the arginine pathway. I named the gene that had mutated
argR, I supposed that argR controlled the production
of an “aporepressor,” arginine being
the “corepressor.” After my return to New York University in the
fall, 1 mapped the argR gene as well as several genes
of the arginine biosynthetic pathway. The results of
these studies were presented at the 1961Cold Spring
Harbor Symposium (MAAS 1961). At the same meeting, GORINIpresented his work on argR mutants
which he had isolated by another, more complicated
method (GORINI, GUNDERSEN
and BURGER196 1).The
Operon Model was also described at this meeting by
JACOB and MONOD(196 1). One of the unusual features
of the arginine system was that, in contrast to the
genes of other biosynthetic pathways (tryptophan, histidine), its genes were not next toeach other butwere
scatteredoverthechromosome,
yet were all controlled by the same regulator gene. Itwas shown that
the tryptophan genes and the
histidine genes were
united in single operons, but the argininegenes were
present in several operons. A. J. CLARK and I, in a
paper demonstrating the dominance of repressibility
over nonrepressibility in diploids (MAASand CLARK
1964), introduced the term “regulon” to describe the
situation of the argininegenes. This paperestablished
clearly that the control of the arginine pathway is
negative via a repressor, the product
of the geneargR.
The nature of the arginine repressor and its targets: In 1961 the general outline of how the synthesis
of enzymes is regulated had been established, thanks
largely to genetic experiments, and now it became
necessary to fill in details in different systems. For
example, the chemical nature of repressors was not
known, and it was also not known whether they
worked at the level of transcription or translation or
even post-translationally (MAAS and MCFALL1964).
These questions were answeredduring the 1960s and
1970s for many systems, including the arginine system. It was shown that repressors are proteins and
that they act at the level of transcription. Their targets, the operator sites, are short, specific DNA sequences located close to the promoters of the regulated genes. In the case of arginine, the question was
raised whether arginine or a derivative of arginine is
the corepressor.Afterconsiderableefforts
it was
shown thatarginine itself is the corepressor. The
developments that occurred in the study of arginine
regulation in prokaryotes up to 1985 have been reviewed by CUNINet al. (1986).
Since then, the argR gene of E. coli K12 has been
cloned and sequenced and the arginine repressor protein has been isolated and its interactions with its
operator sites analyzed (LIMet al. 1987). Several unusual features distinguish the arginine repressor from
other repressors. It appears tobe a hexamer,whereas
other repressors are either dimers or tetramers. Its
target site consists of two 18-bp palindromicsequences
(ARG boxes) located near each other within the promoter region of each gene of the arginine regulon.
Recently, co-crystals of the repressorprotein with
synthetic ARG boxes have been obtained by JOACHIMIAK in SIGLER’S
laboratory at Yale University and
are being subjected to X-ray diffraction analysis. Studies on the interaction of the arginine repressor with
its operator sites have thus reached thelevel ofatomic
resolution.
Another feature of the argininesystem is of general
interest. It had already been notedin 1961 by GORINI
that theregulation of arginine synthesis is different in
E. coli B and E. coli K12 (ENNISand GORINI 1961).
493
Perspectives
During growth in the absence of added arginine,
endogenously produced arginine brings aboutthe
same degree of repression of the arginine enzymes
(about 90%) in both strains. With added arginine, the
arginine enzymes of E. coli K 12 are totally repressed,
whereas the arginine enzymes of E. coli B are only
about 80% repressed. Later, this difference was shown
by J A c o B Y and GORINI (1967) and by us (KADNERand
MAAS1971) to be due to different argR alleles in the
two strains. Recently, DONCBIN
LIM inour laboratory
has cloned and sequenced the argR gene of E. coli B
and has isolatedthe arginine repressor from this strain
(LIM et al. 1988). The B repressor differs by one
amino acid from the K12 repressor but some of its
properties, such as solubility,are quite different. The
question is, how could the difference between the two
repressors account for the observed difference in the
regulation of enzyme synthesis by arginine?
We have now found a partial answer to this question. It should be recalled that the active repressor
consists of the ArgR protein (aporepressor) and arginine (corepressor). The degree of repression is therefore determined by the concentrations of repressor
protein and arginine. Limiting either canlead to
derepression. The formation of the K12 repressor is
autoregulated (LIMet al. 1987) and there is presumptive evidencethat this is also true for the B repressor.
In fact, it appears that autoregulation by the B repressor is so strong that the repressor concentration
can become limiting for repression, so that derepressionof OTCase andother arginine enzymesmay
ensue. When the operator and promoter sites of the
B repressor are removed and replaced by the potent
tac promoter, which does not have the argR operator
sites, the addition of arginine brings about complete
repression, as it does with the K12 argR gene. After
induction with the inducer IPTG, presumably more
repressor protein is produced with the tac promoter
than with the normal argR promoter.
These findings raise an interesting question. Why
should a wild-type strain of E. coli increase the level
of arginine-forming enzymes when it is supplied with
external arginine? So far I have no clear answer for
this paradoxical situation, but the persistence ofE. coli
B in nature suggests that there must be a selective
advantage for B-type regulation of arginine biosynthesis in the ecological niche occupied by E. coli B. If
we do find an answer, we may uncover new principles
that apply to the regulation of gene expression in
general. Thus, even after 35 years of investigation,
the regulation of arginine biosynthesis raises challenging questions for futureresearch.
The author is grateful for continuous supported since 1958 by
I’ublic Health Service Grant GM-06048 from the National Institute
for General Medical Sciences for studies on the regulation of
arginine biosynthesis.
LITERATURE CITED
BROCK,T. D., 1990 The Emergence of BacterialGenetics, Chapter
10. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.
BURNET,
M., 1959 The Clonal Selection Theory of Acquired Immunity,
pp. 50-51. Vanderbilt University Press, Nashville, Tenn.
CUNIN, R., N. GLANSDORFF,
A. PIERARD
and V. STALON,
1986 Biosynthesis and metabolism of arginine in bacteria.
Microbiol. Rev. 50: 314-352.
ENNIS,H. L., and L. GORINI,1961 Control of arginine biosynthesis in strains of Escherichia coli not repressible by arginine.
J. Mol. Biol. 3: 439-446.
FRUTON,
J. S., and S. SIMMONDS,
1953 General Biochemistry. John
Wiley It Sons, New York.
GORINI,L., W. GUNDERSEN
and M. BURGER,1961 Genetics of
regulation of enzyme synthesisin thearginine biosynthetic
pathway of Escherichia coli. Cold Spring Harbor Symp. Quant.
Biol. 2 6 173-182.
GORINI,L., and W. K. MAAS,1957 The potential for the formation of a biosynthetic enzyme in Escherichia coli. Biochim.
Biophys. Acta 25: 208-209.
HAUROWITZ,
F., 1952 The mechanism of the immunological response. Biol. Rev. 27: 247-280.
JACOB,F., and J. MONOD,1961 On the regulation of gene activity.
Cold Spring Harbor Symp. Quant. Biol. 2 6 193-21 1.
JACOBY, G. A., and L. GORINI,1967 Genetics of control of the
arginine pathway in Escherichia coli B and K. J. Mol. Biol. 2 4
4 1-50.
JUDSON, H. F., 1970 The Eighth Day of Creation, Chapter 7. Simon
It Schuster, New York.
KADNER,
R. J., and W. K. MAAS,1971 Regulatory gene mutations
affecting arginine biosynthesisin Escherichia coli. Mol. Gen.
Genet. 111: 1-14.
LEDERBERG,J.,1956 Comments on gene-enzyme relationships,
pp. 161-162 in Enzymes: Units of Biologzcal Structure and FuncAcademic Press, New York.
tion, edited by 0. H. GAEBLER.
LIM, D., J. D. OPPENHEIM,
T. ECKHARDT
and W. K. MAAS,
1987 Nucleotide sequence of the argR gene of Escherichia coli
K-12 and isolation of its product, the arginine repressor. Proc.
Natl. Acad. Sci. USA 84: 6697-6701.
LIM,D., J. OPPENHEIM,
T. ECKHARDTand W. K. MAAS,
1988 The
unitary hypothesis for the repression mechanism of arginine
biosynthesis in E. coli B and E. coli K12 revisited after 18 years,
pp. 55-63 in Gene Expression and Regulation: The
Legacy of Luigi
Gorini, edited by M. BISSELL,G. DEHO,G . SIRONIand A.
TORRIANI.
Excerpta Medica, New York.
MAAS, W.K., 1956 Regulation of arginine biosynthesis in Escherichia coli. Biol. Bull. 111: 319.
MAAS,W. K., 1961 Studies on repression of arginine biosynthesis
in Escherichia cola. Cold Spring Harbor Symp. Quant. Biol. 26:
183-191.
MAAS,W. K., 1974 Some thoughts on the regulation of arginine
biosynthesis and its relation to biochemistry, pp 399-403 in
Lippmann Symposium: Energy, Biosynthesis andRegulationin
Molecular Biology, edited by D. RICHTER.Walter de Gruyter,
New York.
MAAS,W. K., and A. J. CLARK,1964 Studies on the mechanism
of repression of arginine biosynthesisin Escherichia coli. 11.
Dominance of repressibility in diploids. J. Mol. Biol. 8: 365370.
MAAS,W. K., and B. D. DAVIS,1952 Production of analtered
pantothenate-synthesizing enzyme by a temperature-sensitive
mutant of Escherichia coli. Proc. Natl. Acad. Sci. USA 38: 785797.
MAAS,W. K . , and L. GORINI,1958 Negative feed-back control of
the formation of biosynthetic enzymes, pp. 15 1- 158 in Physiological Adaptation, edited by C. L. PROSSER.American Physiological Society, Washington, D.C.
494
W. K. Maas
MAAS,W. K., and E. MCFALL,1964 Genetic aspects of metabolic
control. Annu. Rev. Microbiol. 18: 95-110.
MONOD,
J., 1956 Remarks on the mechanismof enzyme induction, p. 26 in Enzymes: Units of Biological Structure and Function,
edited by 0. H. GAEBLER.
Academic Press, New York.
MONOD,
J., 1966 From enzymatic adaptation to allosteric transitions. Science 154: 475-483.
A., and L. SZILARD, 1950 Description of the chemostat.
NOVICK,
Science 112: 715-716.
K. F., 1974 Logic of discovery and justification in
SCHAFFNER,
regulatory genetics. Stud. Hist. Philos. Sci. 4: 349-385.
J. H., andW. K. MAAS,1960 Analysisof the inhibition
SCHWARTZ,
of growth produced by canavanine in Escherichia coli. J. Bacterial. 7 9 794-799.
SCHWARTZ,
J. H., W. K. MAAS and E. J. SIMON,1959 An impaired
concentrating mechanism for amino acids in mutants of Escherichia coli resistant to L-canavanine and Dserine. Biochim.
Biophys. Acta 32: 582-583.
SZILARD,
L., 1960 The control of the formation of specific proteins in bacteria and in animal cells. Proc. Natl. Acad. Sci. USA
4 6 277-29 1.
VOGEL,H. J., 1953 On growth-limiting utilization of a-N-acetylL-ornithine. Proc. 6th Int. Congr. Microbiol. (Rome) 1: 269271.
VOGEL,H. J., 1957 Repression and induction as control mechanisms of enzyme biogenesis: the “adaptive” formation of acetylornithinase, pp 276-289 in The Chemical Basis of Heredity,
edited by W. D. MCELROY
and B. GLASS.The Johns Hopkins
Press, Baltimore.