RPL7 interacts with RNA and is involved in ribosome biogenesis and the regulation of mRNA translation. One of these proteins is RPL7 which is located at the surface of the large (60S) ribosomal subunit (referred in the recent nomenclature to as RP元0 ). Interestingly, several host proteins potentially interacting with Gag have been identified. This prompted us to look for host chaperoning factors cooperating with GagNC. Along this line, GagNC was also shown to hardly anneal primer tRNA Lys,3 to the Primer Binding Site (PBS), thus causing a profound defect in viral DNA synthesis.
However, it was found that GagNC chaperone activity was low as compared to the mature NCp7 protein present in infectious virions. This FL RNA dimerization is driven by the nucleic acid chaperone activity of GagNC that directs structural rearrangements of nucleic acid molecules which rapidly reach their most stable structure. The FL RNA has a long 5′ untranslated region (UTR) containing a specific packaging signal composed of four stem-loops that mediate the binding of the NC domain of Gag (GagNC) and subsequently the formation of a dimeric FL RNA genome present in the viral particle. The Gag polyprotein precursor is formed of several domains that are the matrix (MA), capsid (CA), nucleocapsid (NC) and p6 as well as the spacer peptides p2 and p1 flanking NC. The second platform corresponds to the phospholipid bilayer of the plasma membrane in which Gag-FL RNA complexes are progressively anchored by the N-terminus of the Gag matrix (MA) domain. The first one is thought to be the FL RNA acting as a scaffold for Gag oligomerization upon binding. In infected cells, Gag orchestrates virion formation in a process that necessitates two platforms. Once exported from the nucleus to the cytoplasm, the FL RNA can be recruited by active ribosomes to direct synthesis of the Gag and GagPol precursors. In HIV-1 infected cells, the integrated viral DNA is transcribed by the host cell machinery generating the full-length viral RNA (also referred to FL RNA), a large fraction of which undergoes splicing to give rise to single and multi-spliced viral mRNAs. Our results show that GagNC interacts with the ribosomal protein RPL7 endowed with nucleic acid chaperone activity, favoring the notion that RPL7 could be a Gag helper chaperoning factor possibly contributing to the start of Gag assembly.
In addition, Gag and RPL7 can function in concert to drive rapid nucleic acid hybridization. Interestingly, RPL7 is shown for the first time to exhibit a potent DNA/RNA chaperone activity higher than that of Gag. This interaction is mediated by the NC zinc fingers and the N- and C-termini of RPL7, respectively, but seems independent of RNA binding, Gag oligomerization and its interaction with the plasma membrane. Here we report that RPL7, a major ribosomal protein involved in translation regulation, is a partner of Gag via its interaction with the NC domain. This prompted us to search for GagNC co-factors. However the RNA chaperoning activity of unprocessed Gag is low as compared to the mature NC protein. This in turn would cause FL RNA dimerization by the NC domain of Gag (GagNC).
Virion formation is orchestrated by Gag, and the current view is that a specific interaction between newly made Gag molecules and FL RNA initiates the process.
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In HIV-1 infected cells, the integrated viral DNA is transcribed by the host cell machinery to generate the full length HIV-1 RNA (FL RNA) that serves as mRNA encoding for the Gag and GagPol precursors.