title: The gammaretroviral p12 protein has multiple domains that function during the early stages of replication.
abstract: BACKGROUND
  The Moloney murine leukaemia virus (Mo-MLV) gag gene encodes three main structural proteins, matrix, capsid and nucleocapsid and a protein called p12. In addition to its role during the late stages of infection, p12 has an essential, but undefined, function during early post-entry events. As these stages of retroviral infection remain poorly understood, we set out to investigate the function of p12.
  
  
  RESULTS
  Examination of the infectivity of Mo-MLV virus-like particles containing a mixture of wild type and mutant p12 revealed that the N- and C-terminal regions of p12 are sequentially acting domains, both required for p12 function, and that the N-terminal activity precedes the C-terminal activity in the viral life cycle. By creating a panel of p12 mutants in other gammaretroviruses, we showed that these domains are conserved in this retroviral genus. We also undertook a detailed mutational analysis of each domain, identifying residues essential for function. These data show that different regions of the N-terminal domain are necessary for infectivity in different gammaretroviruses, in stark contrast to the C-terminal domain where the same region is essential for all viruses. Moreover, chimeras between the p12 proteins of Mo-MLV and gibbon ape leukaemia virus revealed that the C-terminal domains are interchangeable whereas the N-terminal domains are not. Finally, we identified potential functions for each domain. We observed that particles with defects in the N-terminus of p12 were unable to abrogate restriction factors, implying that their cores were impaired. We further showed that defects in the C-terminal domain of p12 could be overcome by introducing a chromatin binding motif into the protein.
  
  
  CONCLUSIONS
  Based on these data, we propose a model for p12 function where the N-terminus of p12 interacts with, and stabilizes, the viral core, allowing the C-terminus of p12 to tether the preintegration complex to host chromatin during mitosis, facilitating integration.
authors.affiliation: Division of Virology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Wight
authors.forename: Virginie C
authors.initials: VC
authors.lastname: Boucherit
authors.forename: Mirella
authors.initials: M
authors.lastname: Nader
authors.forename: David J
authors.initials: DJ
authors.lastname: Allen
authors.forename: Ian A
authors.initials: IA
authors.lastname: Taylor
authors.forename: Kate N
authors.initials: KN
authors.lastname: Bishop
mesh_terms: D004252:DNA Mutational Analysis; D015683:Gene Products, gag / Q000235:genetics* / Q000378:metabolism*; D017989:Leukemia Virus, Gibbon Ape / Q000235:genetics / Q000502:physiology; D008979:Moloney murine leukemia virus / Q000235:genetics / Q000502:physiology*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication
chemical_list: C468293:Gag protein p12, moloney murine leukemia virus; D015683:Gene Products, gag; D050505:Mutant Proteins