Multiple transcripts of the mouse tyrosinase gene are generated by alternative splicing

Abstract

We report the cloning and isolation of the mouse tyrosinase cDNA by screening mouse B16 melanoma cDNA libraries. Independent cDNA clones have been characterized by restriction enzyme analysis, hybridizations with individual subprobes and by partial sequencing analysis. Based on these criteria we have identified multiple transcripts, which in comparison to the major transcript, display deletions of internal sequences and have different 3' termini. The most abundant transcript encodes a functional tyrosinase. The structural gene which encodes five exons separated by large introns and spans a chromosomal region of approximately 70 kb has been isolated. Comparison of the cDNAs with the cloned genomic DNAs and sequencing of the exon/intron boundaries reveal that the multiple transcripts are generated by alternative splicing and putatively by alternate polyadenylation site usage. The alternative splicing mechanisms involve exon skipping as well as internal donor splice site usage. Primer extension analysis shows that the transcripts are produced from two different promoters. Southern blot analysis of DNAs derived from mice carrying the lethal albino deletion mutations demonstrates that the structural gene maps near or at the albino locus. The viable albino mouse BALB/c carries an apparently intact structural gene indicating that the albino phenotype is a consequence of a failure to express the tyrosinase gene or the inability to produce a tyrosinase enzyme.