The nucleotide sequence of a rat liver glutathione S-transferase subunit cDNA clone.

Abstract

We have determined the nucleotide sequence of a cloned cDNA derived from liver poly(A) RNA of pentobarbital-treated rats encoding a glutathione S-transferase subunit.This cDNA clone pGTR261 contains one open reading frame of 222 amino acids, a complete 3' noncoding region, and 63 nucleotides in the 5' noncoding region.The cloned DNA hybridizes to rat poly(A) RNA in a tissue-specific fashion, with strong signals to liver and kidney poly(A) RNA(s) of -1100 and -1400 nucleotides in size but little or no hybridization to poly(A) RNAs from heart, lung, seminal vesicles, spleen, or testis under stringent conditions.Our sequence covers the cDNA sequence of pGST94 which contains a partial coding sequence for a liver glutathione S-transferase subunit of Y, size.Comparison of sequences with our earlier clone pGTR112 suggests that there are at least two mRNA species coding for two different subunits of the Y,, (Mr = 25,600) subunit family with very limited amino acid substitutions mainly of conserved polarity.The divergent 3' noncoding sequences should be useful molecular probes in differentiating these two different but otherwise very similar subunits in induction and genomic structure analyses.Our results suggest that tissue-specific expression of the glutathione S-transferase subunits represented by the sequences of pGTR261 and pGTRl12 may occur at or prior to the level of RNA processing.The glutathione S-transferases (EC 2.5.1.18)are a group of dimeric multifunctional proteins in drug biotransformation and xenobiotics metabolism (1-3).Their activities are induced to a higher level by many xenobiotics including phenobarbital (4, 5 ) .This isozyme family exhibits the following activities:1) catalysis of GSH conjugation to a variety of hydrophobic compounds with electrophilic centers, for example, l-chloro-2,4-dinitrobenzene, benzo(a)pyrene-7,8-epoxide, etc. (6); 2) selenium-independent GSH peroxidase activity toward organic hydroperoxides such as lipid and steroid hydroperoxides (7-12).Rat liver glutathione S-transferases have been reported to exist in multiple forms; however, there is uncertainty regarding the exact number of isozymes and extent of multiplicity in the constituent subunits as well as the precise