Isolation of a cDNA coding for human galactosyltransferase

Human milk galactosyltransferase (EC 2.4.1.22) was purified to homogeneity using affinity chromatography. Edman degradation was used to determine the amino acid sequences of eight peptide fragments isolated from the purified enzyme. A 60-mer "optimal" oligonucleotide probe that corresponded to the amino acid sequence of one of the galactosyltransferase peptide fragments was constructed and used to screen a lambda gt10 cDNA library. Two hybridization-positive recombinant phages, each with a 1.7 Kbp insert, were detected among 3 X 10(6) recombinant lambda gt10 phages. Sequencing of one of the cDNA inserts revealed a 783 bp galactosyltransferase coding sequence. The remainder of the sequence corresponded to the 3'-region of the mRNA downstream from the termination codon.