Abstract
The amino acid sequence of .beta.-galactosidase [EC 3.2.1.23] was determined. The protein contains 1021 amino acid residues in a single polypeptide chain. The subunit MW calculated from the sequence is 116,248. The sequence determination, carried out mainly by conventional methods, was aided by complementation tests, by the use of termination mutant strains and by a new immunochemical method. The 5 residue sequence Thr-Pro-His-Pro-Ala appears twice within the polypeptide chain, but no other striking homologous features are evident.