A sequence-specific DNA-binding protein recognising a GA-rich element cooperates with Oct-1 at the herpes simplex virus type 1 IE3 promoter.

Herpes simplex virus immediate early (IE) gene transcription is regulated via the upstream TAATGARAT motif and involves the recruitment of the ubiquitous octamer-binding protein Oct-1 and a component of the virion Vmw65 into a multiprotein complex termed the immediate early complex (IEC). An upstream GA-rich element (GA-RE) has been postulated to mediate a response to Vmw65 independent of TAATGARAT. We have studied IEC formation in gel shift assays using DNA fragments containing these sequence elements from the HSV-1 IE gene 3 promoter in different combinations. The results show that a factor which footprints to the GA-RE cooperates with Oct-1 to increase IEC levels on a TAATGARAT motif located 5 bp 5' to the GA-RE. The factor alone is unable to promote IEC formation. We were unable to demonstrate any effect of this factor on a TAATGARAT motif located 16 bp from the GA-RE, suggesting that this effect is not universal for all TAATGARAT motifs.