Autosomal albino chicken mutation (c(a)/c(a)) deletes hexanucleotide (-Delta GACTGG817) at a copper-binding site of the tyrosinase gene

We compared tyrosinase cDNA sequences from a line of autosomal albino and B lack Silky chickens isolated from cultured melanocytes by reverse transcrip tion-polymerase chain reaction (RT-PCR). Both sources produce a single DNA fragment of predicted normal tyrosinase size. Direct sequencing of the PCR product showed three mutated sites in the tyrosinase gene of the albino chi cken. Two silent point mutations and a deletion of six nucleotides (-Delta GACTGG) at 817 bp in the tyrosinase cDNA sequence were observed when compar ed with the White Leghorn and Black Silky cDNA sequences. The deduced albin o chicken tyrosinase protein lacks two amino acids, aspartic acid and trypt ophan. The position of these amino acids is consistent with one of the pote ntial copper-binding sites that should be indispensable for function of the enzyme. We speculate that the six-base deletion is responsible for the ina ctive tyrosinase in this line of albino chickens.