Page 1 \ ?^p 6r.1 CELL CYCLE CONTROL OF HUMAN H4 ...

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Progression irom a 9€m cell to an adult o.ganism is mediated by the
complex interplay ol many gen€ €gulatory progiams. These programs contror
prollleraton tom a singlo c€l lo a multicelular organism wilh dislincl
sp€clalized tissues composed of d ifefonl cell types. The col s n each lissue
6xprsss uniqus ssts ot genos, whichaf€ charact€rislic oi either prolirerating of
dlriersntialod cslls.cell prolilgrarlon is a mul!.st€p procsss (revjewed in
Baserqa, 1945; cross er a/., 1949; Muray and Kirschner, 1989i Pardee,1989;
weinberg, 1989; Lovine, 1990). Ihe plocess ot c6ll diuisio^ is chaiacterized by
a sequental series of biochemical evenls thar is tir$ aimed at the replication or
the sukaryotjc genome during S-phase (Se€ Fig- 1)- Subsequenlly, mulliple
ch.omosomes a€ segregated in an ofdsrly manner, a.i passed on to two
daughter ells as a resulr ol miross. Th€ malntenance oi chfomatin slrlc1lre
during the various phas€s ol th6 c6ll cycl€ is vefy lmponant ror the preciss
sepaGton of the tuo sets oi chromosomes. The inkctness of the
chromosomes ls reqlired lor completion of the norrnal celL grovih process,
The strucruraL organizarlon ol ONA wirhin lhs nucleus ls medialed by histone
Hisione synthesis d uring rhe cell cycle
Histone genes musl b€ express€d in a highly efficie.r manner to
accomodare a very rapid rat€ hislon€ p.otein synhssis. lt can b6 calcular€d
thal, ior each subtype, severallholsand copies arc needed for each round ot
ceLldivision. Thus,lhe celular p.orein synlhssls machinery is ded cal€d lo the