An isolated polynucleotide which contains a polynucleotide sequence selected from the group comprising: (a) a polynucleotide which is at least 70% identical to a polynucleotide coding for a polypeptide containing the amino acid sequence of SEQ ID No. 2, (b) a polynucleotide coding for a polypeptide containing an amino acid sequence which is at least 70% identical to the amino acid sequence of SEQ ID No. 2, (c) a polynucleotide which is complementary to the polynucleotides of (a) or (b), and (d) a polynucleotide containing at least 15 consecutive nucleotides of the polynucleotide sequence of (a), (b) or (c), and a fermentation process for the preparation of L-amino acids using corynebacteria in which at least the pknB gene is amplified, and to the use, as hybridization probes, of polynucleotides containing the sequences according to the invention.