[Show abstract][Hide abstract] ABSTRACT: We identified a cDNA encoding a putative cytosolic sulfotransferase (SULT) by searching the expressed sequence tag database of Bombyx mori, and subsequently obtained the full-length cDNA for this gene via rapid amplification of cDNA ends (RACE). We designated this gene bmST1, and showed by sequence analysis that it belongs to a novel SULT family. The tissue specificity of bmST1 mRNA expression was examined in fifth instar larvae by reverse transcriptase-polymerase chain reaction (RT-PCR), and transcripts were detectable in the silk gland, gut, fat body, and Malpighian tube. A recombinant form of bmST1 was then expressed using a gluthathione S-transferase (GST) gene fusion system, and it was purified from Escherichia coli. Purified bmST1 did not exhibit sulfating activity toward SULT substrates such as 4-nitrophenol, vanillin, hydroxysteroids, or monoamines. Surprisingly, however, recombinant bmST1 showed considerable activity toward 4-nitrocatechol and also gallate esters, although the catechins are not sulfated by this enzyme.