Distinctive structure of the human GSTM3 gene - Inverted orientation relative to the mu class glutathione transferase gene cluster

The sequence and exon-intron structure of the human class mu GSTM3 glutathi one transferase gene and its orientation with respect to the remainder of t he human class mu GSTM gene cluster were determined. The GSTM 13 gene is 28 47 bp long and is thus considerably shorter than the other class mu genes i n the cluster, which range in size from 5325 to 7212 bp. Outside the protei n-coding region, the GSTM3 gene does not share significant sequence similar ity with other class mu glutathione transferase genes. Identification of ov erlapping cosmid clones that span the region between GSTM5 the next nearest glutathione transferase gene, and GSTM3 showed that the two genes are abou t 20,000 bp apart. PCR primers developed from sequences 3'-downstream from the GSTM5 gene were used to identify clones containing the GSTM3 gene. Ampl ification with these primers showed that the orientation of the GSTM3 gene is 5'-GSTM5-3'3'-GSTM3-5'. Long-range PCR reactions confirmed this orientat ion both in the GSTM-YAC2 YAC clone, which contains the five class mu gluta thione transferase genes on chromosome 1, and in human DNA. This tail-to-ta il orientation is consistent with an evolutionary model of class mu glutath ione transferase divergence from a pair of tail-to-tail "M1-like" and 'M3-l ike" class mu glutathione transferase genes that was present at the mammali an radiation to the current organization of multiple head-to-tail M1-like g enes tail-to-tail with a single M3-like gene with distinct structural prope rties and expression patterns. (C) 1999 Academic Press.