title: The matrix domain contributes to the nucleic acid chaperone activity of HIV-2 Gag.
abstract: BACKGROUND
  The Gag polyprotein is a multifunctional regulator of retroviral replication and major structural component of immature virions. The nucleic acid chaperone (NAC) activity is considered necessary to retroviral Gag functions, but so far, NAC activity has only been confirmed for HIV-1 and RSV Gag polyproteins. The nucleocapsid (NC) domain of Gag is proposed to be crucial for interactions with nucleic acids and NAC activity. The major function of matrix (MA) domain is targeting and binding of Gag to the plasma membrane but MA can also interact with RNA and influence NAC activity of Gag. Here, we characterize RNA binding properties and NAC activity of HIV-2 MA and Gag, lacking p6 domain (GagΔp6) and discuss potential contribution of NC and MA domains to HIV-2 GagΔp6 functions and interactions with RNA.
  
  
  RESULTS
  We found that HIV-2 GagΔp6 is a robust nucleic acid chaperone. HIV-2 MA protein promotes nucleic acids aggregation and tRNA(Lys3) annealing in vitro. The NAC activity of HIV-2 NC is affected by salt which is in contrast to HIV-2 GagΔp6 and MA. At a physiological NaCl concentration the tRNA(Lys3) annealing activity of HIV-2 GagΔp6 or MA is higher than HIV-2 NC. The HIV-2 NC and GagΔp6 show strong binding to the packaging signal (Ψ) of HIV-2 RNA and preference for the purine-rich sequences, while MA protein binds mainly to G residues without favouring Ψ RNA. Moreover, HIV-2 GagΔp6 and NC promote HIV-2 RNA dimerization while our data do not support MA domain participation in this process in vitro.
  
  
  CONCLUSIONS
  We present that contrary to HIV-1 MA, HIV-2 MA displays NAC activity and we propose that MA domain may enhance the activity of HIV-2 GagΔp6. The role of the MA domain in the NAC activity of Gag may differ significantly between HIV-1 and HIV-2. The HIV-2 NC and MA interactions with RNA are not equivalent. Even though both NC and MA can facilitate tRNA(Lys3) annealing, MA does not participate in RNA dimerization in vitro. Our data on HIV-2 indicate that the role of the MA domain in the NAC activity of Gag differs not only between, but also within, retroviral genera.
authors.affiliation: Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland. kasiapw@ibch.poznan.pl.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Pachulska-Wieczorek
authors.affiliation: Institute of Computing Science, Poznan University of Technology, Piotrowo 2, 60-965, Poznan, Poland.
authors.forename: Leszek
authors.initials: L
authors.lastname: Błaszczyk
authors.affiliation: Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland.|Institute of Computing Science, Poznan University of Technology, Piotrowo 2, 60-965, Poznan, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Biesiada
authors.affiliation: Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland.|Institute of Computing Science, Poznan University of Technology, Piotrowo 2, 60-965, Poznan, Poland.
authors.forename: Ryszard W
authors.initials: RW
authors.lastname: Adamiak
authors.affiliation: Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland. purzycka@ibch.poznan.pl.
authors.forename: Katarzyna J
authors.initials: KJ
authors.lastname: Purzycka
mesh_terms: D015498:HIV-2 / Q000502:physiology*; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism*; D009994:Osmolar Concentration; D012357:RNA, Transfer, Lys / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D012357:RNA, Transfer, Lys; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; D012965:Sodium Chloride
keywords: Gag; HIV-2; Matrix; Nucleic acid chaperone; Nucleocapsid; RNA binding proteins; RNA dimerization; RNA structure; tRNALys3 annealing