5'-upstream structure of the gene coding for chicken riboflavin-binding protein and its relation to estrogen induction.

To elucidate the mechanism of the estrogen-dependent induction of chicken riboflavin-binding protein (RfBP), we analyzed the 5'-upstream structure of its gene. A noncoding exon exists there, and around this sequence, 9 widely spaced half-palindromic estrogen-response element (ERE) motifs (5'-GGTCA or 5'-TGACC) were found. Furthermore, an imperfect ERE-like palindromic sequence (5'-ATGTCANNNTGACAT-3') was also found at the 2.25 kb upstream region. No consensus palindromic ERE was observed. By luciferase reporter assay, the regions containing the half ERE motifs and the imperfect ERE showed estrogen-dependent enhancer activities, suggesting that these two characteristic sequences might confer estrogen-inducibility upon the chicken RfBP gene. However the activities were lower than that of a consensus ERE. It remains uncertain whether these sequences act cooperatively.