Archaeal RNA polymerase: the influence of the protruding stalk in crystal packing and preliminary biophysical analysis of the Rpo13 subunit

Multisubunit DNA-Dependent RNA Polymerases from Vaccinia Virus and Other Nucleocytoplasmic Large-DNA Viruses: Impressions from the Age of Structure

The past 17 years have been marked by a revolution in our understanding of cellular multisubunit DNA-dependent RNA polymerases (MSDDRPs) at the structural level. A parallel development over the past 15 years has been the emerging story of the giant viruses, which encode MSDDRPs. Here we link the two in an attempt to understand the specialization of multisubunit RNA polymerases in the domain of life encompassing the large nucleocytoplasmic DNA viruses (NCLDV), a superclade that includes the giant viruses and the biochemically well-characterized poxvirus vaccinia virus. The first half of this review surveys the recently determined structural biology of cellular RNA polymerases for a microbiology readership. The second half discusses a reannotation of MSDDRP subunits from NCLDV families and the apparent specialization of these enzymes by virus family and by subunit with regard to subunit or domain loss, subunit dissociability, endogenous control of polymerase arrest, and the elimination/customization of regulatory interactions that would confer higher-order cellular control. Some themes are apparent in linking subunit function to structure in the viral world: as with cellular RNA polymerases I and III and unlike cellular RNA polymerase II, the viral enzymes seem to opt for speed and processivity and seem to have eliminated domains associated with higher-order regulation. The adoption/loss of viral RNA polymerase proofreading functions may have played a part in matching intrinsic mutability to genome size.

Lysine methylation mapping of crenarchaeal DNA-directed RNA polymerases by collision-induced and electron-transfer dissociation mass spectrometry

Enzymatic machineries fundamental for information processing (e.g., transcription, replication, translation) in Archaea are simplified versions of their eukaryotic counterparts. This is clearly noticeable in the conservation of sequence and structure of corresponding enzymes (see for example the archaeal DNA-directed RNA polymerase (RNAP)). In Eukarya, post-translational modifications (PTMs) often serve as functional regulatory factors for various enzymes and complexes. Among the various PTMs, methylation and acetylation have been recently attracting most attention. Nevertheless, little is known about such PTMs in Archaea, and cross-methodological studies are scarce. We examined methylation and N-terminal acetylation of endogenously purified crenarchaeal RNA polymerase from Sulfolobus shibatae (Ssh) and Sulfolobus acidocaldarius (Sac). In-gel and in-solution protein digestion methods were combined with collision-induced dissociation (CID) and electron-transfer dissociation (ETD) mass spectrometry analysis. Overall, 20 and 26 methyl-lysines for S. shibatae and S. acidocaldarius were identified, respectively. Furthermore, two N-terminal acetylation sites for each of these organisms were assessed. As a result, we generated a high-confidence data set for the mapping of methylation and acetylation sites in both Sulfolobus species, allowing comparisons with the data previously obtained for RNAP from Sulfolobus solfataricus (Sso). We confirmed that all observed methyl-lysines are on the surface of the RNAP.

Transcriptomic analysis of the SSV2 infection of Sulfolobus solfataricus with and without the integrative plasmid pSSVi

The fusellovirus SSV2 and the integrative plasmid pSSVi, which constitute a unique helper-satellite virus system, replicate in Sulfolobus solfataricus P2. In this study, we investigated the interplay among SSV2, pSSVi and their host by transcriptomic analysis. Following infection of S. solfataricus P2, SSV2 activated its promoters in a temporal and distributive fashion, starting from the transcription of ORF305. Expression of several host genes encoding DNA replication and transcription proteins was up-regulated, suggesting that SSV2 depended heavily on the host replication machinery for its replication. SSV2 gene expression appeared to follow a similar pattern in S. solfataricus P2 harboring pSSVi to that in S. solfataricus P2 lacking the plasmid. Several early genes of the virus were transcribed earlier and more efficiently in the presence of pSSVi than in its absence. These results provide valuable clues to the understanding of the three-way interactions among SSV2, pSSVi and the host.

Game on, science - how video game technology may help biologists tackle visualization challenges

The video games industry develops ever more advanced technologies to improve rendering, image quality, ergonomics and user experience of their creations providing very simple to use tools to design new games. In the molecular sciences, only a small number of experts with specialized know-how are able to design interactive visualization applications, typically static computer programs that cannot easily be modified. Are there lessons to be learned from video games? Could their technology help us explore new molecular graphics ideas and render graphics developments accessible to non-specialists? This approach points to an extension of open computer programs, not only providing access to the source code, but also delivering an easily modifiable and extensible scientific research tool. In this work, we will explore these questions using the Unity3D game engine to develop and prototype a biological network and molecular visualization application for subsequent use in research or education. We have compared several routines to represent spheres and links between them, using either built-in Unity3D features or our own implementation. These developments resulted in a stand-alone viewer capable of displaying molecular structures, surfaces, animated electrostatic field lines and biological networks with powerful, artistic and illustrative rendering methods. We consider this work as a proof of principle demonstrating that the functionalities of classical viewers and more advanced novel features could be implemented in substantially less time and with less development effort. Our prototype is easily modifiable and extensible and may serve others as starting point and platform for their developments. A webserver example, standalone versions for MacOS X, Linux and Windows, source code, screen shots, videos and documentation are available at the address: http://unitymol.sourceforge.net/.

Archaeal transcription: making up for lost time

In recent years, emerging structural information on the aRNAP (archaeal RNA polymerase) apparatus has shown its strong evolutionary relationship with the eukaryotic counterpart, RNA Pol (polymerase) II. A novel atomic model of SshRNAP (Sulfolobus shibatae RNAP) in complex with dsDNA (double-stranded DNA) constitutes a new piece of information helping the understanding of the mechanisms for DNA stabilization at the position downstream of the catalytic site during transcription. In Archaea, in contrast with Eukarya, downstream DNA stabilization is universally mediated by the jaw domain and, in some species, by the additional presence of the Rpo13 subunit. Biochemical and biophysical data, combined with X-ray structures of apo- and DNA-bound aRNAP, have demonstrated the capability of the Rpo13 C-terminus to bind in a sequence-independent manner to downstream DNA. In the present review, we discuss the recent findings on the aRNAP and focus on the mechanisms by which the RNAP stabilizes the bound DNA during transcription.

Soaking of DNA into crystals of archaeal RNA polymerase achieved by desalting in droplets

Transcription is a fundamental process across the three domains of life and is carried out by multi-subunit enzymatic DNA-directed RNA polymerases (RNAPs). The interaction of RNAP with nucleic acids is tightly controlled for precise and processive RNA synthesis. Whilst a wealth of structural information has been gathered on the eukaryotic Pol II in complex with DNA/RNA, no information exists on its ancestral counterpart archaeal RNAP. Thus, in order to extend knowledge of the archaeal transcriptional apparatus, crystallization of Sulfolobus shibatae RNAP (molecular mass of ~400 kDa) with DNA fragments was pursued. To achieve this goal, crystal growth was first optimized using a nanoseeding technique. An ad hoc soaking protocol was then put into place, which consisted of gently exchanging the high-salt buffer used for apo-RNAP crystal growth into a low-salt buffer necessary for DNA binding to RNAP. Of the various crystals screened, one diffracted to 4.3 Å resolution and structural analysis showed the presence of bound DNA [Wojtas et al. (2012). Nucleic Acids Res. 40, doi:10.1093/nar/gks692].

Structural and functional analyses of the interaction of archaeal RNA polymerase with DNA

Multi-subunit RNA polymerases (RNAPs) in all three domains of life share a common ancestry. The composition of the archaeal RNAP (aRNAP) is not identical between phyla and species, with subunits Rpo8 and Rpo13 found in restricted subsets of archaea. While Rpo8 has an ortholog, Rpb8, in the nuclear eukaryal RNAPs, Rpo13 lacks clear eukaryal orthologs. Here, we report crystal structures of the DNA-bound and free form of the aRNAP from Sulfolobus shibatae. Together with biochemical and biophysical analyses, these data show that Rpo13 C-terminus binds non-specifically to double-stranded DNA. These interactions map on our RNAP–DNA binary complex on the downstream DNA at the far end of the DNA entry channel. Our findings thus support Rpo13 as a RNAP–DNA stabilization factor, a role reminiscent of eukaryotic general transcriptional factors. The data further yield insight into the mechanisms and evolution of RNAP–DNA interaction.