Altered salivary amylase gene in the mouse strain BXD-16

An electrophoretic salivary amylase variant in the recombinant inbred mouse strain BXD-16 segregated in crosses as an allele at the salivary amylase locus. No other strain was found with the same combination of electrophoretic types of salivary and pancreatic amylase, and no sign of contamination by foreign genes from other strains was found. The variant therefore seems to have arisen during the inbreeding of the strain by a genetic alteration in the amylase complex. Purified variant amylase had a lower heat stability and an altered net charge of one or more CNBr fragments, but had the same size distribution of peptides from restricted proteolysis and CNBr cleavage as salivary amylase from the progenitor strains. Radioactive pulse labelling of the variant amylase showed that its relative rate of synthesis was the same as that in the progenitor strains. The variant is therefore, most likely, the result of a missense mutation that has altered the structure of all the salivary amylase produced in the strain. This indicates that only a single structural gene for the enzyme is expressed in the strain BXD-16.