Identification of nuclear factors that bind to the mouse tyrosinase gene regulatory region

Several nuclear factors that interact with sequences in the 5' flanking region of the mouse tyrosinase gene were identified using band shift and methylation interference assays. One of these factors bind to an AT-rich sequence, TATCAATTAG, located at -183 base pairs upstream of the transcription start site. To isolate cDNA clone encoding this DNA binding protein, we have screened a lambda gt11 cDNA expression library prepared from mouse melanocyte cell line with a labeled oligonucleotide probe containing its binding site. Complementary DNA clones encoding mouse high mobility group protein HMG-I and its isoform HMG-Y were obtained. HMG-I(Y) is a low molecular size, basic nuclear protein that binds specifically to AT-rich region of double-stranded DNA in vitro. In Northern blot analysis the level of HMG-I(Y) mRNA expression did not correlate with that of tyrosinase or TRP-1. Although the amount of HMG-I(Y) transcripts has no apparent influence on the mouse tyrosinase gene expression, it is possible that HMG-I(Y) binds to the 5' flanking sequence of the tyrosinase gene as an auxiliary factor, and facilitates the binding and activity of other transcription factors.