An isolated polynucleotide comprising a polynucleotide sequence selected from the group consisting of

a) polynucleotide which is at least 70% identical to a polynucleotide that codes for a polypeptide which comprises the amino acid sequence of SEQ ID No. 2,

b) polynucleotide which codes for a polypeptide that comprises an amino acid sequence which is at least 70% identical to the amino acid sequence of SEQ ID No. 2,

c) polynucleotide which is complementary to the polynucleotides of a) or b), and

d) polynucleotide comprising at least 15 successive nucleotides of the polynucleotide sequence of a), b) or c),

and processes for the fermentative preparation of L-amino acids using coryneform bacteria in which at least the metH gene is present in enhanced form, and use of the polynucleotide sequences as hybridization probes.