POSITIVE AND NEGATIVE REGULATION AT THE HERPES-SIMPLEX VIRUS ICP4 ANDICP0 TAATGARAT MOTIFS

The control of the ICP0 and ICP4 immediate early genes of herpes simpl ex Virus (HSV) can critically determine the course of viral lytic or l atent infections. Their promoters contain so-called TAATGARAT motifs t hat are activated via a multiprotein complex which includes cellular p roteins Oct-1 and HCF and the viral activator VP16 (=Vmw65, alpha TIF) . Relative to the ICP4 promoter TAATGAGAT sequence, the ICP0 promoter motif has a 5' extension that includes a full octamer sequence (ATGCTA ATGATAT). It seemed possible that this overlapping octamer site might render the ICP0 promoter element more active by allowing tighter bindi ng of the Oct-1/VP16 complex or more vulnerable to repression by other Oct proteins. Our experiments favor the former possibility. On the on e hand, the extended ICP0 site shows stronger binding of the Oct-1/VP1 6 complex compared to the ICP4 site. Moreover, transcription of a repo rter gene with multiple ICP0 sites is strongly activated by VP16 in tr ansfected cells. On the other hand, the ICP0 site is largely refractor y toward repression by a different Oct factor (N-Oct2 = Bm1) which com petes with Oct-1/VP16 for the site. In marked contrast, multiple copie s of the conventional TAATGAGAT motif of ICP4 are poorly activated by VP16, and transcription from this site can be completely repressed by N-Oct2. However, inclusion of the neighboring CGGAAR motifs from the I CP4 promoter, which bind factors GABP alpha and beta, results in a str ong synergistic activation. This activity, like that of the complete I CP4 promoter, becomes refractory to repression by competing N-Oct2. Th us the standard TAATGARAT motif of ICP4 is by itself less active and m ore vulnerable to repression than the extended ICP0 motif, and its act ivation depends upon synergism with neighboring DNA sites and their co gnate factors. This difference between the two types of TAATGARAT moti fs may allow for a more complex transcriptional regulation by factor c ombinations. (C) 1995 Academic Press, Inc.