Transcription apparatus of the yeast killer DNA plasmids: Architecture, function, and evolutionary origin

Abstract

ABSTRACTTranscription of extrachromosomal elements such as organelles, viruses, and plasmids is dependent on cellular RNA polymerase (RNAP) or intrinsic RNAP encoded by these elements. The yeastKluyveromyces lactiscontains killer DNA plasmids that bear putative non-canonical RNAP genes. Here, we describe the architecture and evolutionary origin of this transcription machinery. We show that the two RNAP subunits interactin vivo, and this complex interacts with another two plasmid-encoded proteins - the mRNA capping enzyme, and a putative helicase which interacts with plasmid-specific DNA. Further, we identify a promoter element that causes 5’ polyadenylation of plasmid-specific transcriptsviaRNAP slippage during transcription initiation, and structural elements that precede the termination sites. As a result, we present a first model of the yeast killer plasmid transcription initiation and intrinsic termination. Finally, we demonstrate that plasmid RNAP and its promoters display high similarity to poxviral RNAP and promoters of early poxviral genes, respectively.