ELEMENTS REGULATING DIFFERENTIAL ACTIVITY OF CHICKEN HISTONE H1 GENE PROMOTERS

The chicken genome contains six closely related histone HI genes, each of which encodes a different H1 protein. The four common regulatory e lements previously identified in H1 histone promoters are very similar in sequence and location in all chicken HI genes, which gives rise to the question of how the six H1 variants are expressed at significantl y different levels. Transient transfections of reporter gene transcrip tional fusions indicate that approximately 200 bp of each promoter is sufficient to generate the observed spectrum of HI promoter activity. The differences in HI promoter-driven expression are shown to be expla ined by the relative activity of the previously characterized G box re gion and that of a novel element found between CCAAT and TATA that we have termed differential upstream sequence (Dus). Gel shift analysis i ndicated that the primary nuclear binding protein to the G box is one or more avian homologues of the Spl transcription factor, The Dus regi on binds multiple nuclear proteins, one of which is the recently descr ibed IBR/IBF factor. The differential affinities of the G box and Dus sequences of the HI promoters for their respective nuclear binding fac tors correlate well with their relative promoter activities.