5 1 2s Biochemical Society Transactions ( 1 996) 24
OF PROTEM S l
WIRIM R?UI FROM RNA BAcTERIOpHdOBs.
Dilara M.Isaeva. Inetitute of Yiorobiologg.
Baku, Azerbaijan
It is known that on phage RNda there i e only
one 'antry'eite for the ribosome - the h t i ation region of the ooat protein g e m . 3 S rib0EiOlnd Bubunit6 are able
ize this
site even in the a b s e n o e t z f r E g t o r tRNd,
but protein S l appear6 to be strongly needed
for the reooepletion prooees..
We have investigated where S l binde to phage
UAEIwithin 305 preinitiation oomplexes formed in t h e abeenoe of initiator tRNA. R e s a t e
o r sequenoing allow us to determine w i t h i n
the phage RHA primarg atruorure the l o m t i o n
of S1-bound fragmente. All the f
, the
major and minor O r U 3 6 , b e l O n g to aZ:'region of phage RNA eequenoe rshioh ie looated upstream from the ooat protein gene:h the oaBe
of QB RNB this re ion oomprieea nuoleotides
1247-1322. with fhe ooat protein intiation
oodon being at 1344; Fn the 0888 of fr RNA
nuoleotides 1226-1297 and 1336. oorrespondinglg. The region proteotid by oovalently bound S1 againet de iation with RNam Ti oompletelg overlape 8 t h the so oalled 5-site Q$
r e p l i o m e binding. S1 ia known to be a tramlstional repreasor o r the ooat protein eintheeie
UCtTO Prom our data this effeot a m be
explained a6 ampetition between free S1 and
S1 as a part of the 305 subunit for the aame
on the messenger. We propose that the aitea
oontaining oligo(U) sequenoea in Qp and Ir
RNda ,serve as reoo
tion signals r o r 305 riboeomee during ini%tion
oomplex formation.
A 1 3 SI'PB-SPECIPIC IN"gRdWI0N
A14
DIFFERENTIAL CELL CYCLE ARREST AND
APOPTOSIS FOLLOWING INDUCIBLE
EXPRESSION OF THE CYCLIN DEPENDENT
KINASE INHIBITOR p21 CIPl IN HUMAN
CELLS
Alexander B. Niculescu I11 .Ludger Hengst,
Monique Smeets,and Steven I.Reed
(Dept. of Molecular Biology,The Scripps
Research lnstitute,La Jolla,CA 92037,USA)
The p21 CiplIWafl Cyclin dependent kinase
inhibitor has been implicated in G1 arrest
following irradiation,as well as in maintaining
terminally arrested,differentiated cells in
GO/Gl.The G1 arrest is mediated by inhibiting
the Cdk dependent phosphorylation of the
retinoblastoma protein,Rb.We sought to
understand better these effects,and
additionally what effects p21 might have
in S phase and G2/M,by expressing p21 in a
panel of human cell lines using a tetracycline
controlled inducible system,as well as
using an adenoviral transduction vector.
Our results concerning our observations of
differential cell cycle arrest,apoptosis,and the
underlying biochemical mechanisms of these
effects will be presented.
A1 6
STATHMIN EXPRESSION IS ASSOCIATED WITH THE
ABILITY OF CELLS TO PROGRESS THROUGH THE CELL
CYCLE. ,Simon S. Guest, David C.
Rowlands*, Kai-M Toellner, Neil A. Jones, Ian C.M.
MacLennaa and Geoffrey Brown. Department of Immunology,
University of Birmingham Medical School, Birmingham B15
2lT. *Department of Pathology, University of Birmingham
Medical School, Birmingham, B15 2'lT.
Stathmin is a prominent cytosolic protein which can be
phosphorylated by MAP kinase, CAMP-dependent protein
kinase and p34& kinase. Immunostaining of human and mouse
tissues has revealed that stathmin is expressed in the
proliferative compartment of cells of most, if not all, cell
lineages. The myeloid cell liaes HL60 and K562 express
stathmin at very high levels. When these cells are induced to
differentiate, stathmin expression is down-regulated as cells go
out of cycle. A decrease in the proportion of stathmin that is
phosphorylated was also observed. To investigate the role that
stathmin plays in the control of cell proliferation, we have
transfected the promonoqtoid cell line U937 with the pMep4
vector containing stathmin cDNA in an antisense orientation.
Antisense stathmin rransfected cells were unable to undergo
normal cell division and became multinucleate. Belmont and
Mitchison (Cell 1996, 84, 623431) have shown in Virro that
stathmin interacts with tubulin dimers to increase the
catastrophe rate of microtubules and suggest that stathmin may
increase the catastrophe rate of microtubules during mitosis.
The above findings show that stathmia plays an important role
in the progression of cells through cycle.
A1 6 CLONING AND PARTIAL CHARACTERISATIONOF
A NOVEL X E N O P U S B-TYPE CYCLIN.
Jane A. IQ&
and Tim Hunt
ICRF Clare Hall Laboratories,
south Mimms,
Potters Bar,
Hertfordshire, EN6 3LD. U.K.
B-type cyclins and their associated kinases play a key role
in controlling progression of cells through mitosis. Four B-type
mitotic cyclins have prcviously been identified in Xenopus laevis.
We used a 320 base pair fragment spanning the cyclin box of the
chicken cyclin B3 ( Gallant and Nigg 1994 ) to probe an oocyte
library and have cloned, sequenced and partially characterised a
novel Xenopus loevis B-type cyclin. The 1.6 kb cDNA clone
has a single open reading frame of 1247 base pairs encoding a
protein with a predicted molecular weight of 47 kDa. When
transcribed and translated in vitro this protein runs as a 50 kDa
protein on SDS-PAGE.
We termed this cyclin XLB3 as it shows significant
sequence homology with chicken B3 cyclin. This chicken cyclin
B3 has characteristics of both A and B-type cyclins. It has
sequence similarity to known B-type cyclins but its protein
product is localised to the nucleus - a characteristic of A-type
cyclins.
There is a putative nuclear localisation signal indicated in
Xenopus B3 by sequence homology to the NLS identified in
chicken B3. A myc-tagged XLB3 expression construct has been
made and studies are ongoing to investigate the localisation of the
protein in transfccted cos-1 cells. To further study XLB3,
polyclonal rabbit antibodies are beiig raised against the
expressed protein.
Gallant P. and Nigg E.A. (1994) Identification of a novel
vertebrate cyclin: cyclin B3 shares properties with both A- and Btype cyclins. The EMBO Journal. 13 (3) 595-600.