INHERITED SOMATIC MOSAICISM CAUSED BY AN INTRACISTERNAL A-PARTICLE INSERTION IN THE MOUSE TYROSINASE GENE

A recessive, fully penetrant mutation (c(m1OR)) at the mouse albino lo cus that results in coat-color mottling has been characterized at the molecular level. Restriction mapping and DNA sequencing analyses provi de evidence that mutants carry a 5.4-kb intracisternal A particle (IAP ) element insertion upstream of the tyrosinase (Tyr) promoter. Norther n blot analysis and reverse transcription-PCR results show that the ty rosinase gene is expressed at much lower levels in mutant than in wild -type mice. The mutant Tyr gene still retains the tissue-specific expr ession pattern, and the Tyr transcript is not initiated from the IAP l ong terminal repeat promoter. We propose that the IAP insertion isolat es the promoter of the tyrosinase gene from upstream cia-acting regula tory elements, leading to a substantially decreased level of Tyr gene expression in mutants.