DEDUCED AMINO-ACID-SEQUENCE, GENE STRUCTURE AND CHROMOSOMAL LOCATION OF A NOVEL HUMAN CLASS MU GLUTATHIONE-S-TRANSFERASE, GSTM4

The Mu-Class glutathione S-transferases (GSTs) are subject to marked i nter-individual variation in man, owing to the fact that 40-50% of the population fail to express M1 subunits. Mu-Class GST from two lymphob lastoid cell lines (expressing M1 subunits and the other 'nulled' for M1) have been studied. Both cell lines were found to express a Mu-Clas s GST that has. not been described previously. The cDNA encoding this novel transferase, designated 'GSTM4', has been isolated and the enzym e shown to be comprised of 218 amino acids (including the initiator me thionine residue) with an M(r) of approx. 25.5 kDa. Molecular cloning demonstrated that the lymphoblastoid cell line which expressed GSTM1 p ossessed the b allelic variant (i.e. that with an asparagine residue a t position 173). The genes for GSTM4 and GSTM1b have been cloned and f ound to contain seven introns and eight exons. The coding region of th e GSTM4 gene, including the seven introns, encompasses 5.0 kb, whereas the same region of GSTM1b is 5.5 kb; the difference in the size of th e two genes is due to the length of intron 7. DNA sequencing allowed a GSTM4-gene-specific oligo-primer to be designed which has been utiliz ed in a PCR-based assay to determine that the GSTM4 gene is located on chromosome 1.