A CIS-ACTING ELEMENT INVOLVED IN MOUSE TYROSINASE GENE-EXPRESSION AND PARTIAL-PURIFICATION OF ITS BINDING-PROTEIN

The tyrosinase gene is specifically expressed in melanocytes. Understanding the molecular basis of tissue-specific expression of the tyrosinase gene will greatly explain the mechanisms controlling pigmentation. We report a nucleotide sequence, TGATGTATTC, located -236 base pairs upstream of the transcription start site, that enhances tyrosinase gene expression in mouse melanoma cells. The sequence is referred to as the tyrosinase element-1 (TE-1). TE-1 was protected from DNase I cleavage by pigment cell nuclear extracts but was not protected by non-pigment cell nuclear extract. Partial purification of TE-1 binding protein (TEBP-1) was performed from the B16 mouse melanoma cell nuclear extract using biotin-cellulose affinity chromatography. The affinity-purified fraction exhibited binding to the DNA fragment containing TE-1, and to a synthetic oligomer representing TE-1. UV-cross-linking indicated that the size of TEBP-1 is approximately 49 kD. TE-1 also directed enhanced CAT activity in the B16 melanoma cells but not in non-pigment cells. These data indicate that TE-1 may be an enhancer element that is responsible for pigment cell specific expression of the tyrosinase gene.