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SUMMARY:Restructuring of bacteriophage ɸ6 viral particle activates semi-c
 onservative transcription
DTSTART:20240416T121500
DTEND:20240416T131500
DTSTAMP:20260406T084358Z
UID:dd4d3611d7afc3cb6d0e006c827324dc614783d061dffa9a1c0b34e2
CATEGORIES:Conferences - Seminars
DESCRIPTION:Juha T. Huiskonen\, Institute of Biotechnology\, Helsinki Inst
 itute of Life Science HiLIFE\, University of Helsinki\, Finland\nDouble-st
 randed RNA viruses transcribe their genome within a proteinaceous viral ca
 psid to avoid host cell defenses. Members of the Reovirales use conservati
 ve transcription analogously to cellular gene expression. Most other dsRNA
  viruses\, however\, transcribe their genome using semi-conservative trans
 cription whereby the positive strand of the genomic template becomes mRNA.
  Here\, we visualize the activation of semi-conservative transcription in 
 ɸ6 cystovirus particles using cryo-EM and Localized Reconstruction method
  (Ilca et al. 2015). The tri-segmented dsRNA genome is organized as a spoo
 l (Ilca et al. 2019). Upon transcription initiation\, we observe a stepwis
 e assembly of transcription complexes at the opposing poles of the genome 
 spool\, in addition to a concomitant expansion of the inner capsid layer a
 nd uncoating of the outer capsid layer. We show that the minor protein P7 
 is essential for transcription. The mature transcription complexes consist
  of asymmetric dimers of P7 dimers forming a triskelion around the viral p
 olymerases (Fig. 1). The polymerases neighbor the vertices of the icosahe
 dral capsid. The packaging hexamers at the vertices channel the viral mRNA
  exit. Our results define the complex molecular pathway from the quiescent
  state to the activation of semi-conservative intra-capsid transcription.\
 n\n\nFig. 1 dsRNA bacteriophage ɸ6 in transcribing state.\nThe viral part
 icle is shown along the 3-fold axis of symmetry. The front half of the two
  capsid layers is removed to reveal the transcription initiation complex a
 nd the spooled dsRNA genome.\n\nSerban L. Ilca1\,2\, Xiaoyu Sun3\, Esa-Pek
 ka Kumpula4\, Katri Eskelin3\, David I. Stuart2\, Minna M. Poranen3\, Juha
  T. Huiskonen2\,4\n1 New York Structural Biology Center\, Simons Electron 
 Microscopy Center\, New York\, NY\, USA\n2 Division of Structural Biology\
 , Centre for Human Genetics\, University of Oxford\, Oxford\, UK\n3 Molecu
 lar and Integrative Biosciences Research Programme\, Faculty of Biological
  and Environmental Sciences\, University of Helsinki\, Helsinki\, Finland\
 n4 Institute of Biotechnology\, Helsinki Institute of Life Science HiLIFE\
 , University of Helsinki\, Helsinki\, Finland\n\nReferences:\nIlca\, S.L.\
 , Kotecha\, A.\, Sun\, X.\, Poranen\, M.M.\, Stuart\, D.I.\, and Huiskonen
 \, J.T. (2015). Localized reconstruction of subunits from electron cryomic
 roscopy images of macromolecular complexes. Nat Commun 6\, 8843.\nIlca\, S
 .L.\, Sun\, X.\, El Omari\, K.\, Kotecha\, A.\, de Haas\, F.\, DiMaio\, F.
 \, Grimes\, J.M.\, Stuart\, D.I.\, Poranen\, M.M.\, and Huiskonen\, J.T. (
 2019). Multiple liquid crystalline geometries of highly compacted nucleic 
 acid in a dsRNA virus. Nature 570\, 252-256.\n\nKeywords: semi-conservativ
 e transcription\, cryo-EM\, localized reconstruction\, symmetry relaxation
 \, dsRNA virus\, bacteriophage\nSupported by: Research Council of Finland 
 and Sigrid Jusélius Foundation\n\n 
LOCATION:SG 1138 https://plan.epfl.ch/?room==SG%201138
STATUS:CONFIRMED
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