A mouse
tyrosinase cDNA has been combined with different promoters and inserted into several replication-competent
avian leukosis proviruses and the viruses were transferred into cultured albino chick cells by
viral infection. Expression of the
tyrosinase gene depended on one of four promoter sequences: the resident constitutive promoter (Rous sarcoma virus long-terminal repeat; RSV-LTR), 471 bp from the mouse
tyrosinase gene-associated promoter, 519 bp from the Japanese quail
tyrosinase gene associated promoter, or 369 bp from the quail
tyrosinase promoter. The infected cells expressed
tyrosinase and produced pigment which could be seen with the light microscope. Immunofluorescence microscopy, using an anti mouse
tyrosinase T1-specific antibody, also showed the presence of mouse
tyrosinase. When infected with the same viral titer, gene expression was highest with the constitutive LTR promoter. The quail
tyrosinase promoter, while less efficient than the LTR, was more efficient than the other
tyrosinase promoter. Fibroblasts and hepatocytes infected with the construct carrying the constitutive promoter or the truncated quail promoter expressed
tyrosinase. The mouse and quail promoters appeared to show tissue-specific expression since fibroblasts and hepatocytes infected with viruses carrying these promoters did not express mouse
tyrosinase. Toxicity is associated with constitutive expression of
tyrosinase in nonmelanocytes. Therefore the viruses that carry the tissue specific promoters should be useful for in vivo studies.