Characterization and heterospecific expression of cDNA clones of genes in the maize GSH S-transferase multigene family

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Abstract
We have isolated from a constructed λgt11 expression library two classes of cDNA clones encoding the entire sequence of the maize GSH S-transferases GST I and GST III. Expression of a full-length GST I cDNA in E. coli resulted in the synthesis of enzymatically active maize GST I that is immunologically indistinguishable from the native GST I. Another GST I cDNA with a truncated N-terminal sequence is also active in heterospecific expression. Our GST III cDNA sequence differs from the version reported by Moore et al. [Moore, R. E., Davles, M. S., O'Connell, K. M., Harding, E. I., Wiegand, R. C, and Tiemeier, D. C. (1986) Nucleic Acids Res. 14:7227–7235] in eight reading frame shifts which result in partial amino acid sequence conservation with the rat GSH S-transferase sequences. The GST I and GST III sequences share ˜45% amino acid sequence homology. Both the GST I and the GST III mRNAs contain different repeating motifs in front of the initiation codon ATG. Multiple poly(A) addition sites have been identified for these two classes of maize GSH S-transferase messages. Genomic Southern blotting results suggest that both GST I and GST III are present in single or low copies in the maize (GT112 RfRf) genome.