A novel piscine vitellogenin gene: structural and functional analyses of estrogen-inducible promoter

The Oreochromis aureus vitellogenin, OaVtg, gene spans 9 kb and contains 34 exons. Its transcription start site is located 15 bp upstream of the trans lational start codon. Although the OaVtg promoter has a nonconsensus TATA, transient transfection assay showed that this promoter is capable of drivin g basal transcription. Two imperfect estrogen response elements: EREp (prox imal) and EREd (distal) are located in the promoter at - 532 and - 1352, re spectively. In competition gel mobility-shift assays, only EREp exhibited s pecific binding of the recombinant estrogen receptor protein, GST-C/D OaER. Another imperfect ERE (EREexon2) was detected within exon 2 of the OaVtg g ene. This is a novel finding for a vitellogenin (Vtg) gene. EREexon2 simila rly showed specific recognition of GST-C/D OaER. Both EREp and EREexon2 sho wed comparable binding affinities as consensus ERE. In transient transfecti ons, the OaVtg promoter, EREp and EREd elicited significant increase in est rogen-dependent synthesis of CAT protein. Hence, we propose that the non-co nsensus OaVtg EREs contribute to the estrogen-dependent regulation of the O aVtg gene in vivo. (C) 1998 Elsevier Science Ireland Ltd. All rights reserv ed.