Résumé
Short RNA species that encompas the ψ domain of the retroviral genome spontaneously form dimers in vitro, and the retroviral nucleocapsid protein activates this dimerization in vitro. Addition of gag RNA sequences downstream of the 3′ end of the ψ domain decreases the level of spontaneous dimerization. Here, we report the effects of RNA length on dimerization in vitro, studied with RNA fragments from Moloney murine leukamia virus that contain the ψ domain and all or part of the gag sequence. Extension of the RNA leads to progressive inhibition of the in vitro dimerization process. Sequences located downstream of the 3′ end of the ψ domain seem to stabilize the monomeric structures. This stabilization participates in dimerization of the RNA sequences involved in the recognition of two RNA molecules. We studied the ability of nucleocapsid protein 10 to promote dimerization of such long RNA fragments, and found that the protein greatly enhances their dimerization in vitro. We propose that nucleocapsid protein 10 stimulates the overall dimerization process by reduction of the energy barrier that must be overcome to allow dimer formation. Our results show that dimerization of RNA form Moloney murine leukaemia virus in vitro is enhanced by nucleocapsid protein 10. This finding is in agreement with the involvement of the nucleocapsid protein in RNA dimerization in vivo.