The structure of two distinct pancreatic amylase genes in mouse strain YBR.

The amylase complex on mouse chromosome 3 encodes both salivary and pancreatic amylase. It appears that one active gene is present for salivary amylase, whereas pancreatic amylase in some strains is coded by at least 4, and perhaps by more than 10, genes. Strain YBR is different from other strains in that it produces twice as much salivary amylase. Pancreatic amylase in YBR is present as two different protein forms, Aβ and Bβ, the sum of which amounts to only one-third of that in, for instance, strain A/J. YBR chromosomal DNA was cloned in phage λ, followed by restriction and heteroduplex analysis of recombinant phages carrying amylase genes. Among 32 phage isolates, 5 carried parts of the salivary amylase sequence. The remaining phage isolates contained pancreatic amylase-like sequences and represented three nonoverlapping genomic regions, i.e., one of 34 kb containing a complete gene, PAN-IIβ; another of 41 kb with a complete but different gene, PAN-Iβ, plus a truncated gene, PAN-ψ1; and finally, one of 23 kb with another truncated gene, PAN-ψ2. Parts of the amino acid sequence of Aβ and Bβ have previously been determined, and we report here the sequencing of a 4-kb DNA fragment from Pan-IIβ which establishes that this gene codes for Bβ.