Multiple initiation and polyadenylation sites for the chicken ovomucoid transcription unit

Abstract A chicken genomic DNA fragment of about 15 ×10 3 bases containing all the ovomucoid gene coding sequences was isolated from a chicken erythrocyte DNA library. The flanking sequences of the ovomucoid gene were analysed by DNA sequencing, and ovomucoid gene transcripts were characterized by nuclease S 1 mapping. Transcription initiates at two sites separated by 85 base-pairs, each site being preceded by a specific promoter sequence for RNA polymerase B. Polyadenylation occurs at three different sites, in all cases downstream from an A-A-T-A-A-A or equivalent signal. The major ovomucoid messenger RNA species has the shortest untranslated regions at both 5′ and 3′ ends. The presence of two promoters, three polyadenylation sites and one previously characterized alternative splicing possibility, all functioning apparently independently, give rise to several functional ovomucoid mRNAs.