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

aziz F: c.tl cy.te cotuot al H4 e$e faNnpll.n
remains to be rssolved is: whd ar6 the Precise tunctional conl.ibutions ol
indivldualGc€gn ton mollls and cognate lactofs i. del.r Ni.ing the l6velot H4
gene rransdiplion in mlltiPle cell rypes? ln parucular, we have obserued
natural s€quenc€ variations in lhe Sit€ ll s€qlences oI diilerenl H4 genes,
which abolish binding ot speci{ic ranscription lacto|s (van wijnen el a/., 1 992)
Ihis raises th€ queston: Does th€ absenc€ ol distinct transcriplion facior
recognilion sites have tunctional consequences for H4 genelransfiplon, and
could rhis anply heterogoneity in transcriPlional regulalion ol dillered H4
genes? In this stldy, we address lhss€ quesllons by syslematicaly anaLyzLng
fie etfecls ol multiple dislinct muiations in each ol lhe Sile ll recognilion motils
on H4lranscrpUon ir vlvo n several cell lypes,
Th€ dbral segment oi Slt€ llls esseniial
lor hlgh levelH4 gens rrarucription
The sequ€nces spanning l|ls distal segment ol Site ll located
immediarely upslream ol the TATA-box in th€ H4 gene (Fig. 5) are highly
consetued among venebrate sp€cies and are also localed in analogols
regions in rh€ promolers ot several other human hisbn€ H4 genes van
winen et a/., 1992). Delerion analyses hav6 shown thal ste ll alone can
suppo.t a low bur signiticanl revel of histooe H4 (Kroeg€r el ar, 1987) or CAf
(Bamsey er a/., 1994) reporter gen€ lranscriplon n the absence ol sl€ I,
which when present sl.ongly augments H4 gene r€nscriplion via inleactions
wirh sPJ and ATF proreins (Bnnbalm dal., 1995). To oblain an €stimale ot
the maximum extent lo which lh€ consetued elemenl i. site ll conkibutes to
H4 gene transcription wlhin rhe native context ol lhe entire proximal promoter,
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