CLONING AND BASE SEQUENCE-ANALYSIS OF A CDNA-ENCODING MOUSE LUNG THIOETHER S-METHYLTRANSFERASE

Thioether S-methyltransferase catalyzes transfer of the methyl group f rom S-adenosylmethionine to X in compounds of the structure R-X-R', wh ere X may be sulfur, selenium, or tellurium, and R and R' may be vario us organic groups. To obtain a cDNA clone of thioether S-methyltransfe rase, a mouse lung cDNA library in lambda Agt11 was screened with a 99 base-pair probe obtained by performing the polymerase chain reaction on oligo(dT) primed, reverse transcribed, mouse lung RNA using two deg enerate primers designed from partial amino-acid sequences of the enzy me. The entire coding and 3'-untranslated regions were obtained and se quenced. The predicted protein contains 264 amino-acid residues and ha s a calculated M(r) of 29 460. The amino-acid sequence of thioether S- methyltransferase contains three motifs characteristic of many methylt ransferases and has a high level of identity with the amino-acid seque nces of nicotinamide N-methyltransferase and phenylethanolamine N-meth yltransferase. However, in spite of the fact that they are both mammal ian cytosolic sulfur methyltransferases, the sequences of thioether S- methyltransferase and thiopurine S-methyltransferase share little iden tity.