Rat liver glutathione S-transferases. DNA sequence analysis of a Yb2 cDNA clone and regulation of the Yb1 and Yb2 mRNAs by phenobarbital.

We have constructed a cDNA clone, pGTA/C48, which is complementary to the rat liver glutathione S-transferase Yb2 mRNA. Recombinant clone pGTA/C48 contains a cDNA insert of 845 base pairs which overlaps nucleotides 108-952 of the Yb1 cDNA clone, pGTA/C44, described previously by our laboratory (Ding, G. J.-F., Lu, A. Y. H., and Pickett, C. B. (1985) J. Biol. Chem. 260, 13268-13271). Over the protein coding region of the Yb1 and Yb2 cDNA clones there is an 84% nucleotide sequence homology, whereas the 3' untranslated regions are only 32% homologous. The complete amino acid sequence of the Yb2 subunit has been determined from a combination of DNA sequence analysis of pGTA/C48 and conventional protein sequence analysis of the glutathione S-transferase Yb1 Yb2 heterodimer. The Yb2 subunit is comprised of 218 amino acids with a molecular weight of 25,705 and has an amino acid sequence which is 79% homologous to the sequence of the Yb1 subunit. We have utilized the divergent 3' untranslated regions of three rat liver glutathione S-transferase cDNA clones as specific probes to determine the effect of phenobarbital on the level of Yb1, Yb2, and Yc mRNAs. Our results clearly show that the Yb1 and Yb2 mRNAs are elevated approximately 5-6-fold by phenobarbital administration; whereas the Yc mRNA is only modestly elevated by this xenobiotic. Finally, our data suggest that the Yb2 subunit is encoded by a gene(s) which is distinct from the Yb1 gene(s) and provides direct evidence for the existence of multiple glutathione S-transferase Yb genes in the rat.