THE REGULATION OF TYROSINASE GENE-TRANSCRIPTION

Tyrosinase is one of the key enzymes essential for melanogenesis. The control of its activity rests in part at the level of transcriptional regulation. The 5' promoter regions of the human, mouse, chicken, quai l, snapping turtle, and frog tyrosinase sequences have been isolated a nd the mechanisms regulating the activity of these sequences are begin ning to be elucidated. This review provides an update on the following aspects of tyrosinase gene regulation: basal promoter elements that d etermine the site of transcription initiation for RNA polymerase II; t he cis-acting elements and DNA-binding factors that mediate melanocyte -specific expression of the tyrosinase gene; promoter elements involve d in the temporal control of tyrosinase gene expression; additional el ements that may be required to achieve wild-type levels of gene expres sion; and specific elements that may be required for modulation of tyr osinase gene expression in response to humoral factors or external sti muli that are known to influence the amounts of melanin synthesized by fully differentiated melanocytes. The wild type expression of tyrosin ase is the result of the interaction of many different factors and it is becoming evident that certain elements and factors play more than o ne role in this process.