The 5' noncoding and flanking regions of the avian very low density apolipoprotein II and serum albumin genes. Homologies with the egg white protein genes.

We have isolated and sequenced the 5' proximal exons and flanking regions of the chicken very low density apolipoprotein II (apo-VLDLII) and serum albumin genes. These genes specify the most abundant mRNA species present in livers of hens or estrogen-treated roosters. Sequencing revealed that the promoter region of the estrogen-dependent apo-VLDLII gene contained at least two potential transcriptional initiation sites, preceded by appropriately positioned "ATA" sequences. One is homologous with the cap site of the ovalbumin gene, and the other exhibits a match of 10 out of 12 nucleotides with the cap site of the serum albumin gene. S1 nuclease mapping indicates that both sites are active in vivo, although the "ovalbumin"-like site is by far the most efficient at all stages of the estrogenic response. The relative efficiencies of these two sites are maintained during in vitro transcription of truncated templates. A third site, that was not anticipated from sequencing data, is active in vivo but inactive in vitro. A conserved 5' flanking element, initially identified during studies on egg white protein genes, is also present upstream from the apo-VLDLII and serum albumin genes. Its removal does not affect initiation site selection in vitro. Regions of the apo-VLDLII and ovalbumin genes extending 100 nucleotides downstream from the "TATA box" contain several striking homologies that suggest a common mode of evolution.