## 3 Results
\begin{table}
\begin{tabular}{l l l l l} \hline
**Strain** & **Value 1, g/L** & **Leucine 1, g/L** & **Isoleucine 1, g/L** & **AHAS Activity 2, Units/mg Protein** \\ \hline VC2 & \(3.6\pm 0.2\) & 0 & 0 & \(1.6\pm 0.3\) \\ VC3 & \(15.6\pm 0.5\) & 0 & 0 & \(10.5\pm 1.5\) \\ VB1 & \(0.44\pm 0.10\) & 0 & 0 & \(13.5\pm 1.5\) \\ VB2 & \(16.2\pm 0.5\) & \(0.5\pm 0.1\) & 0 & \(21.5\pm 2.5\) \\ VB3 & \(24.1\pm 1.0\) & \(1.0\pm 0.1\) & 0 & \(140.0\pm 15.0\) \\ L2.5 & 0 & \(10.0\pm 0.3\) & \(0.5\pm 0.1\) & ND 3 \\ L2.5-\(\textit{{\tiny{\it{\it{\it{\it{\it{\it{\it{\it{\it{\it{\it{   }}}}}}}}}}}}\) & \(15.1\pm 0.5\) & \(10.0\pm 0.3\) & \(0.5\pm 0.1\) & ND 3 \\ \hline \end{tabular}  
* The levels of production of BCAAs are calculated as the average of three experiments. 2 Activity values are calculated as the average of three experiments. 3 ND—no data.  
\end{table} 
Table 2: Effect of the G110A mutation in the regulatory region of the _ilvBNC_ operon at the level of BCAA biosynthesis and AHAS activity in different strains of _C. glutamicum_. A Model for the Transcriptional Regulation of the C. glutamicum ilvBNC Operon and the Computer Modeling of Mutations in It  
We noted above that both [PERSON] et al. [4] and [PERSON] et al. [6] suggested the possibility of the formation of three hairpins in the regulatory region of the _ilvBNC_ operon in _C. glutamicum_, one of which was positioned as a terminator, and the possibility of its formation was confirmed by enzymatic probing [6], but its functionality as a transcription terminator was not proved experimentally, because the deletion of a part of this hairpin did not significantly affect the expression of the operon [4]. The role of the other two hairpins in the mechanism of regulation of the expression of the _ilvBNC_ operon also remains incompletely understood. To analyze the mechanism of transcription attenuation in the regulatory region of the _ilvBNC_ operon, we performed computer calculations of the secondary structure of the attenuator using the programs described in [17; 18]. The calculations confirmed the possibility of formation in the regulatory region of the _ilvBNC_ operon from the three inverted repeats H\({}_{1}\), H\({}_{2}\), and H\({}_{3}\) (Figure 1) of the two most thermodynamically stable mRNA secondary structures, which correspond to the two regulatory states (Figure 3A,B). In the first case, the hairpin H\({}_{1}\) blocks the formation of hairpin H\({}_{2}\) and does not prevent the formation of the terminator hairpin H\({}_{3}\), which leads to transcriptional arrest, and the OFF state occurs (Figure 3A). In the second case, H\({}_{2}\) hairpin formation prevents the formation of the terminator hairpin H\({}_{3}\), as their sequences overlap with each other, and the ON transcription state occurs (Figure 3B). Thus, in terms of role assignment, the H\({}_{1}\) hairpin is an antiantiterminator and the H\({}_{2}\) hairpin is an antiterminator. Antiantiterminator structures in bacterial attenuators have been found previously [21]. It should be noted that the two states described above are difficult to distinguish in comparative analysis and enzymatic probing [6] because the paired nucleotides in the ON and OFF states are often the same. It was noted above that the start of translation in the _ilvBNC_ operon is only one nucleotide away from the start codon of the leader peptide [4]. For bacterial translation initiation, such peptides are characterized by the landing of the ready ribosomal complex in the start codon region, which requires 10-11 nucleotides downstream from the start codon free of complementary interactions [22]. This feature casts doubt on whether the H\({}_{1}\) hairpin can exist in a state of initiated translation, because the H\({}_{1}\) hairpin shields the ribosome  
Figure 2: Effect of the G110A mutation on the transcription level of the _ilvB_, _ilvB_, and _ilvC_ genes in different strains of _C. glutamicum_. The level of gene expression in the strain ATCC 13869 is set to 1. Data are calculated as the average of three experiments.