# Mutational Analysis Supports Three-Hairpin Model of Attenuator for Transcription Regulation of ilvBNC Operon in Corynebacterium glutamicum

## TL;DR

This study reveals how three hairpin structures in the ilvBNC operon regulate gene expression and amino acid production in Corynebacterium glutamicum.

## Contribution

The study proposes a novel model of transcriptional regulation involving three functional mRNA hairpins in the ilvBNC operon.

## Key findings

- Three mRNA hairpins function as a terminator, antiterminator, and antiantiterminator in the ilvBNC operon.
- The terminator hairpin significantly influences operon expression and valine production.
- The attenuator allows rapid transitions between hairpins without full structural disruption.

## Abstract

The ilvBNC operon in Corynebacterium glutamicum encodes key enzymes for the biosynthesis of branched-chain amino acids (L-isoleucine, L-leucine, and L-valine). This operon has been studied for quite a long time, and it is assumed that three hairpin mRNA structures can be formed in its regulatory region; however, their functionality and role in the attenuation mechanism of the ilvBNC operon are not completely clear. In the present work, we performed a mutational analysis of mRNA secondary structures in the regulatory region of the C. glutamicum ilvBNC operon, which allowed us to propose a model of the regulation of its transcription involving three mRNA hairpins that essentially act as a transcription terminator, an antiterminator, and an antiantiterminator. In this work, we proved the existence of a transcription terminator in this operon and experimentally confirmed the effectiveness of its influence on the expression of the ilvBNC operon, AHAS enzyme activity, and valine production. We demonstrated the unique functional features of this attenuator, which, due to the overlapping of the terminator and antiterminator hairpins, is capable of rapid low-energy transitions between them without the complete disruption of the hairpin structures.