Genetics of the serine cycle in Methylobacterium extorquens AM1: cloning, sequence, mutation, and physiological effect of glyA, the gene for serine hydroxymethyltransferase

The gene (glyA) of Methylobacterium extorquens AM1 encoding serine hydroxymethyltransferase (SHMT), one of the key enzymes of the serine cycle for C_1 assimilation, was isolated by using a synthetic oligonucleotide with a sequence based on amino acid sequence conserved in SHMTs from different sources. The amino acid sequence deduced from the gene revealed high similarity to those of known SHMTs. The cloned gene was inactivated by insertion of a kanamycin resistance gene, and recombination of this insertion derivative with the wild-type gene produced an SHMT null mutant. Surprisingly, this mutant had lost its ability to grow on C_1 as well as on C_2 compounds but was still able to grow on succinate. The DNA fragment containing glyA was shown not to be linked with fragments carrying serine cycle genes identified earlier, making it the fourth chromosomal region of M. extorquens AM1 to be indicated as being involved in C_1 assimilation