Maria Sokolova, Arina Drobysheva, Julia Gordeeva and Konstantin Severinov from Skoltech together with AlphaFold Team and other researchers published a preprint “Structural basis of template strand deoxyuridine promoter recognition by a viral RNA polymerase”. The study is focused on phage AR9 non-virion RNA polymerase (nvRMAP). The scientists showed that this enzyme utilizes an unusual mechanism of transcription initiation. nvRNAP recognizes a −10 promoter element in the template strand directly while other bacterial RNA polymerases recognize -10 element via sigma factor. Together, the AR9 nvRNAP sigma-like subunit, the enzyme core, and the template strand itself form two nucleotide base-accepting pockets whose shapes dictate the AR9 nvRNAP’s deoxyuridine promoter requirement. A single amino acid substitution in the promoter specificity subunit allows one of these pockets to accept a thymine base thus expanding the enzyme’s promoter consensus. Full text of the preprint is available here.