S-adenosyl-L-methionine (SAM) is an intermediate metabolite of
methionine and serves as the methyl donor for many
biological methylation reactions. The synthesis of SAM is catalyzed by SAM
synthetase (
SAMS), which transfers the adenosyl moiety of adenosine-5'-triphosphate to
methionine. In the nematode Caenorhabditis elegans, four
sams family genes, sams-1, -3, -4 and -5, are predicted to encode
SAMS proteins. However, their physiological roles remain unclear. Here we show that the four predicted
SAMS proteins in fact have the ability to catalyze the formation of SAM in vitro, and revealed that only sams-1 mutant animals among the family genes exhibited a significant reduction in egg-laying. Using transgenic animals carrying a transcriptional reporter for each
sams gene promoter, we observed that each
sams promoter confers a distinct expression pattern with respect to tissue, time of expression and expression level (i.e. promoter specificity). Promoter-swap experiments revealed that the ectopic expression of SAMS-3, -4 or -5 driven by the sams-1 promoter completely rescued egg-laying in sams-1 mutants. These data indicate that
SAMS protein function is conserved throughout the entire family.