Accepted_test

The adaptation of bacteria to environmental changes has led to their ability to rapidly modulate gene expression in various ways, including RNA-dependent regulation. RNA free energy landscapes translate environmental signals into the language of RNA structural dynamics, which, due to the high specificity and speed of complementary interactions, ensures an immediate reaction of the bacterium. A good example is a special RNA element, an attenuator, which regulates transcription of the ilvBNC operon of Corynebacterium glutamicum, which then determines the biosynthesis of branched chain amino acids (L-isoleucine, L-leucine, L-valine). In this paper, we develop a new model of transcriptional regulation of ilvBNC operon expression, which explains the experimental data obtained on  mutant strains with single nucleotide substitutions in the regulatory region. In this model, the hairpins of the terminator and the antiterminator partially overlap, so that the boundary trinucleotide GCC participates in the formation of both structures. As a result, in the free energy landscape, a valley is formed between the termination and antitermination states, and the attenuator is able to cross it using a sequence of low-energy transitions, thus controlling rapid changes in valine production.