Transcription of extrachromosomal elements such as organelles, viruses, and plasmids is dependent on cellular RNA polymerase (RNAP) or intrinsic RNAP encoded by these elements. The yeast Kluyveromyces lactis contains 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 interact in 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 transcripts via RNAP 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.K2ORF6p regardless of the presence or absence of nucleic acids which was confirmed by PCR ( Supplementary Figure S3).Taken together, the immunoprecipitation, mass spectrometry, and Western blot results demonstrated the existence of the hypothesized plasmid-specific transcription complex because K2ORF3p, K2ORF4p, K2ORF6p, and K2ORF7p were specifically associated in vivo.This association was independent of nucleic acids. Finally, K2ORF3p, K2ORF6p, and K2ORF7p appeared to form a core transcription complex with relatively strong mutual interactions to which K2ORF4p bound relatively weakly.
Putative helicase is associated with plasmid-specific DNA in vivoThe weak binding of K2ORF4p to the other three proteins suggested that the putative helicase may also interact with plasmid DNA. Hence, we performed in vivo chromatin immunoprecipitation. We used the IFO1267_pRKL2-13 strain expressing HA-K2ORF4p and 10.1007/BF00326291, PMID: 2065362 Kämper J, Meinhardt F, Gunge N, Esser K. 1989. In vivo construction of linear vectors based on killer plasmids from Kluyveromyces lactis: selection of a nuclear gene results in attachment of telomeres. Mol Cell Biol 9:3931-3937. 24 Kettenberger H, Armache KJ, Cramer P. 2004. Complete RNA polymerase II elongation complex structure and its interactions with NTP and TFIIS. Mol Cell 16:955-965. Kuznedelov K, Korzheva N, Mustaev A, Severinov K. 2002. Structure-based analysis of RNA polymerase function: the largest subunit's rudder contributes critically to elongation complex stability and is not involved in the maintenance of RNA-DNA hybrid length.