Mechanism of RNA recognition by the M2-1 transcription antiterminator from respiratory syncytial virus (RSV)

SEBASTIAN ESPERANTE; LUCIA CHEMES; DE PRAT GAY GONZALO; IVANA MOLINA

San Francisco

Encuentro; 62th Annual Meeting. Biophysical Society; 2018

Biophysical Society

RNA transcription of mononegavirales decreases gradually from the 3? leader promoter towards the 5? end of the genome, due to a decay in polymerase processivity. In the syncytial respiratory (RSV) and metapneumoviruses, the M2-1 protein, ensures transcription antitermination. Despite being a homotetramer, RSV M2-1 binds two molecules of RNA of 13 nt or longer per tetramer, and temperature sensitive secondary structure in the RNA ligand is unfolded by stoichiometric interaction with M2-1. Fine quantitative analysis show positive cooperativity, indicative of conformational asymmetry in the tetramer. RNA binds to M2-1through a fast bimolecular association followed by slow rearrangements corresponding to an induced-fit mechanism on the protein side. Kinetic data provide a sequential description of time events of cooperativity, where a first binding event of half of the RNA molecule to one of the sites increases the affinity of the second binding event on the adjacent contacting protomer, product of increased effective concentration by the entropic link. This mechanism allows high affinity binding with an otherwise loose sequence specificity, and suggests a structural recognition signature in the RNA for modulating gene transcription. This work provides a basis for the understanding of the mechanism of transcription antitermination, an essential event for explaining transcription polarity in pneumoviruses.