Use of an in vivo reporter assay to test for transcriptional and translational fidelity in yeast

Architecture of the RNA polymerase II-TFIIS complex and implications for mRNA cleavage

The transcription elongation factor TFIIS induces mRNA cleavage by enhancing the intrinsic nuclease activity of RNA polymerase (Pol) II. We have diffused TFIIS into Pol II crystals and derived a model of the Pol II-TFIIS complex from X-ray diffraction data to 3.8 A resolution. TFIIS extends from the polymerase surface via a pore to the internal active site, spanning a distance of 100 A. Two essential and invariant acidic residues in a TFIIS loop complement the Pol II active site and could position a metal ion and a water molecule for hydrolytic RNA cleavage. TFIIS also induces extensive structural changes in Pol II that would realign nucleic acids in the active center. Our results support the idea that Pol II contains a single tunable active site for RNA polymerization and cleavage, in contrast to DNA polymerases with two separate active sites for DNA polymerization and cleavage.

Translesion synthesis by RNA polymerases: occurrence and biological implications for transcriptional mutagenesis

The genes of all organisms are continuously damaged by extrinsic and intrinsic physical and chemical agents. If the resulting DNA damage is left unrepaired, a number of deleterious biological consequences may result including the production of mutant proteins which can change the cellular phenotype. The majority of DNA damage-induced mutagenesis studies are based on models of DNA polymerase errors occurring in the vicinity of the lesion. In contrast, few studies have addressed the possibility that mutagenesis at the level of transcription (i.e. when RNA polymerase bypasses a lesion and a misincorporation event occurs) may also be an important source of mutant proteins, particularly in nondividing cell populations. This article reviews a number of recent studies on translesion synthesis by RNA polymerases resulting in the production of mutant transcripts (transcriptional mutagenesis). Over a dozen different types of DNA damage are now known to be bypassed with various degrees of efficiency and miscoding abilities by the transcriptional elongation machinery. Some important biological implications of transcriptional mutagenesis are discussed.