Elements regulating differential activity of chicken histone H1 gene promoters.

The chicken genome contains six closely related histone H1 genes, each of which encodes a different H1 protein. The four common regulatory elements previously identified in H1 histone promoters are very similar in sequence and location in all chicken H1 genes, which gives rise to the question of how the six H1 variants are expressed at significantly different levels. Transient transfections of reporter gene transcriptional fusions indicate that approximately 200 bp of each promoter is sufficient to generate the observed spectrum of H1 promoter activity. The differences in H1 promoter-driven expression are shown to be explained by the relative activity of the previously characterized G box region and that of a novel element found between CCAAT and TATA that we have termed differential upstream sequence (Dus). Gel shift analysis indicated that the primary nuclear binding protein to the G box is one or more avian homologues of the Sp1 transcription factor. The Dus region binds multiple nuclear proteins, one of which is the recently described IBR/IBF factor. The differential affinities of the G box and Dus sequences of the H1 promoters for their respective nuclear binding factors correlate well with their relative promoter activities.