A point mutation in the tyrosinase gene of BALB/c albino mouse causing the cysteine → serine substitution at position 85

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Abstract
Murine albinism is characterized by complete lack of melanin pigments in skin and retina. In order to study the molecular basis of albinism, we have cloned and characterized the tyrosinase gene of BALB/c mice (c/c). Sequence analysis of this gene reveals a point mutation at nucleotide residue 387 (G → C transversion) causing a Cys→Ser substitution at position 85 in one of the cysteine-rich domains of the tyrosinase molecule. Since this G→C transversion creates an additional DdeI site, we were able to confirm that this mutation is actually present in BALB/c genomic DNA using DNA amplification techniques. In contrast, both C57BL/6 (C/C) and DBA/2 (C C) mouse strains carry the G residue at the same position, suggesting that this point mutation is specific for the albino mutation at the c locus. Moreover, we were able to show that the tyrosinase containing Ser-85 is not functional in transient expression of its cDNA. We therefore suggest that a G→C transversion at nucleotide residue 387 of the tyrosinase gene could lead to the albino phenotype of BALB/c mouse.