Mouse gamma-casein cDNA: PCR cloning and sequence analysis.

A partial amino acid sequence of mouse gamma-casein was determined on a gas-phase amino acid sequencer. The N-terminal sequence (23 residues) was obtained using native gamma-casein, and the C-terminal sequence (13 residues) was determined with a corresponding peptide. The C-terminal peptide was isolated by affinity chromatography on an anhydrotrypsin agarose column after digestion of gamma-casein with Achromobacter lysyl-endopeptidase. A cDNA (507 base pairs) encoding the mature protein of gamma-casein was produced by polymerase chain reaction (PCR) amplification of lactating mammary gland first strand cDNA with oligonucleotide primers designed from the N-terminal (KHEIKDK-) and the C-terminal (-AHYTRFY) amino acid sequences. The full-length cDNA including 5'- and 3'-noncoding regions (920 base pairs) was cloned by the rapid amplification of cDNA ends (RACE) method of Frohman et al. Comparison of full-length cDNAs of mouse gamma-casein and rat gamma-casein showed 80% identity at the nucleotide level. The amino acids in the coding region of both gamma-caseins were 75% identical.