Maria Sokolova, Arina Drobysheva, Julia Gordeeva and Konstantin Severinov from Skoltech have co-authored a recent preprint “Template strand deoxyuridine promoter recognition by a viral RNA polymerase” that has been released at bioRxiv. The paper focuses on the unusual DNA-dependent RNA-polymerase of Bacillus subtilis bacteriophage AR9. The genome of this phage is represented by a double-stranded DNA, but with uracils instead of thymines. AR9 non-virion RNA polymerase has a unique ability to recognize promoters in the template strand of dsDNA and efficiently differentiate obligatory uracils from thymines in its promoters. The scientists have unveiled the molecular details of the catalytic cycle of this unusual enzyme using structural data obtained by cryo-electron microscopy and X-ray crystallography. The researchers elucidated a unique mode of uracil-specific, template strand-dependent promoter recognition. It is achieved by a tripartite interaction between the promoter specificity subunit, the core enzyme, and DNA adopting a unique conformation. Full text of the preprint is available here