## 3 Results  
The Effect of the G110A Mutation in the Regulatory Region of the _ilvBNC_ operon in \(C\). glutamicum Strains  
The initial premise of this research was the detection of a mutation in the _C. glutamicum_ VF strain with increased valine production--a substitution of guanine with adenine at a position \(-\)183 bp upstream of the start of translation of the _ilvB_ gene. As shown in Figure 1, the leader peptide is located upstream of the structure gene of the _ilvBNC_ operon at position 1337840-1337887 bp according to sequence BA000036.3. The point mutation discovered during the whole-genome sequencing of the valine-producing strain _C. glutamicum_ VF (replacement of G with A) is located within the regulatory region at position 1337948(GenBank: BA000036.3)--183 bp upstream of the start codon of the _ilvB_ structural gene outside the leader peptide sequence [8], or 110 bp downstream of the transcription start codon. The _C. glutamicum_ VF strain is derived from the _C. glutamicum_ ATCC 13032 strain and does not have other mutations in the structural genes for valine synthesis (_ilvB_, _ilvN_, _ilvC_, _ilvD_) [8]. The G110A mutation was introduced into various strains originating from _C. glutamicum_ ATCC 13032 and _C. glutamicum_ ATCC 13869, as well as into the _C. glutamicum_ L2.5 strain, a leucine producer obtained by mutagenesis, presumably from the _C. glutamicum_ ATCC 14067 strain. From the results presented in Table 2, it follows that the G110A mutation in all studied strains of _C. glutamicum_ leads to an increase in valine production from 50% to several times compared to the production of the original strain. The G110A mutation did not affect the growth rate of the strains. The optical density at 600 nm (OD\({}_{600}\)) for all strains was approximately 65-72 after 48 h of fermentation. It is interesting to note that the potential of the _C. glutamicum_ strains ATCC 13032 and ATCC 13869 also differs in the level of valine production: a derivative of _C. glutamicum_ ATCC 13869 produces five times more valine than a derivative of _C. glutamicum_ ATCC 13032. Enzymes encoded by the _ilvB_, _ilvN_, and _ilvC_ genes are involved in the biosynthesis of all three BCAAs: valine, leucine, and isoleucine. One would expect that the G110A mutation in the regulatory region of the _ilvBNC_ operon would affect the production of not only valine but also other BCAAs. However, as shown in Table 2, the presence of the G110A mutation in the studied _C. glutamicum_ strains had virtually no effect on the production of isoleucine and had no significant effect on the production of leucine, even in a strain whose metabolism is aimed at its synthesis. The latter may be related to the possibility that the rate-limiting enzyme is not AHAS but another enzyme in the leucine biosynthesis chain. The level of transcription of the _ilvB_, _ilvN_, and _ilvC_ genes in the strains with mutations in the regulatory region of the _ilvBNC_ operon was studied using real-time RT-PCR technology. From the results presented in Figure 2, it can be seen that the introduction of the G110A mutation into the genome of the different strains of _C. glutamicum_ leads to a several-fold increase in the transcription of the _ilvB_ and _ilvN_ genes encoding the subunits of the AHAS enzyme, which in turn leads to an increase in AHAS activity by 6.5 times compared to the parental strains (Table 2). These facts suggest the involvement of the mutation G110A in the attenuator regulation of the transcription of the _ilvBNC_ operon.