A BASIS FOR DIFFERENTIATING AMONG THE MULTIPLE HUMAN MU-GLUTATHIONE S-TRANSFERASES AND MOLECULAR-CLONING OF BRAIN GSTM5

Specific cDNA probes and antisera were employed to interpret genetic p olymorphisms of human Mu-class glutathione S-transferases and to provi de a basis for identifying individual forms in human tissues. A cDNA p robe that cross-hybridized with various human and rodent Mu-glutathion e S-transferase transcripts, hybridized with at least three discrete c omponents by Northern analysis of RNA from human tissue. The smallest (1.3 kb) transcript was identified as the one that encodes GSTM3-3 sub units. A form designated GSTM5, was cloned from a human brain cDNA lib rary and its sequence determined. The open reading frame of GSTM5 shar ed a high degree of homology with the sequences of other Mu-class glut athione S-transferases, but its 846-nucleotide 3'-noncoding region was unique and considerably larger than that of any of the other Mu forms . Specific synthetic peptide antigens were utilized to distinguish amo ng Mu-class glutathione S-transferases in different tissues of represe ntative individuals. The primary hepatic transcript was that encoding GSTM1-1 with much lesser amounts of GSTM3-3, but livers were devoid of GSTM2-2, and GSTM5-5. Immunoblots confirmed that null-phenotype indiv iduals lacked the GSTM1 gene rather than its GSTM2 homologue that is n early identical in its exon sequences. The null phenotype therefore wa s conspicuous in liver, where GSTM1-1 ordinarily was the predominant M u transcript, but brain and testis contained all four forms. A general strategy was devised to distinguish among and assign primary structur es to individual glutathione S-transferases from human tissue.