SUMMARY PARAGRAPH for SHM1
SHM1 encodes the mitochondrial isoform of serine hydroxymethyltransferase (SHMT) (5, 2), an enzyme which reversibly converts serine to the products glycine and 5,10 methylene tetrahydrofolate (CH2-THF). CH2-THF serves as a one-carbon donor for reactions leading into purine, pyrimidine, amino acid, and lipid biosynthesis (3). Shm1p activity comprises only about 5% of the total cellular SHMT activity (4, 3), but it does contribute measurably to glycine biosynthesis when serine is available (4); when serine is limited, Shm1p functions in the direction of serine biosynthesis (3). Consistent with the relatively minor role of this isoform, the shm1 null mutation does not confer any nutritional requirements (4); however, an uncharacterized mutant allele of shm1 (designated tmp3) blocks respiratory growth (5). SHM1 transcription is not highly regulated, in contrast to the cytosolic isoform SHM2 whose transcription responds to glycine and one-carbon compound levels (6, 7).
Shm1p and Shm2p have similarity to other SHMTs, which are conserved from bacteria to humans (4, 8). Mutation of an isoform of SHMT in C. elegans has a maternal effect lethal phenotype (8), and the human ortholog of Shm2p, SHMT1 (OMIM) is implicated in Smith-Magenis syndrome.
Last updated: 2008-01-29