Abstract:

Glutathione S-transferases (GSTs) constitute a multifunctional superfamily in which Zeta class is widely distributed in animals, plants, and bacteria. In mammals, Zeta GSTs show maleylacetoacetate isomerase (MAAI) activity and participate in phenylalanine and tyrosine metabolism. In this study, expressed sequence tags (ESTs) were searched for the predicted GST gene from Bombyx mori, BmGSTz1. A contig containing 1 239 bp was assembled on the basis of ESTs of BmGSTz1, which extended into 3′ and 5′-UTR (untranslated region). The contig of BmGSTz1 perfectly matched to the corresponding region of the silkworm genome sequence and had a poly (A) signal in its 3′-UTR. BmGSTz1 was composed of 4 introns and 5 exons, and the boundary between exon and intron conformed to the canonical GT-AG rule. TA cloning verified that the coding sequence (CDS) was 648 bp in length and encoded 215 amino acids. The putative molecular weight and isoelectric point of BmGSTz1 were 24.8 kD and 8.06, respectively. BmGSTz1 had relatively high similarities with GSTz1 from insects and mammalians. Phylogenetic analysis showed that BmGSTz1, DmGSTz1, AgGSTz1, ApGSTz1, and TcGSTz1 might be 1∶1∶1∶1∶1 orthologues. The RT-PCR and microarray data indicated that BmGSTz1 was expressed in various tissues in Day-3 5th instar silkworm larvae. The results of sequence analysis and expression characterization suggest that BmGSTz1 might have the MAAI activity. The data presented in this study provide useful information for further studying the function of BmGSTz1.

Key words: Bombyx mori, glutathione S-transferases, tyrosine metabolism, sequence analysis, cDNA cloning, expression characterization