Schematic representation of the HIV-1 genome with localization of the RT primer grip domain in Pol. M230A infectivity was highly attenuated (a decrease of approximately 10 4-fold compared to the wild type ), and mutants L234D and W239A were found to be noninfectious, while most other mutants (E224A, P225A, F227A, G231A, E233A, and H235A) showed WT or slightly attenuated infectivity.
![francotte lyon francotte lyon](https://www.lhotellerie-restauration.fr/journal/restauration/2015-11/img/100_3553.jpg)
Three mutants, namely, M230A, L234D, and W239A (Met230 to Ala, Leu234 to Asp, and Try239 to Ala, respectively) retained our attention (Fig. Fig.1), 1), and the effects of these mutations on HIV-1 virus structure and replication were examined. Highly conserved residues in and around the primer grip motif were mutated (see Fig. The HIV-1 RT primer grip domain is highly conserved among several related retroviruses ( 16, 40), and its implication in RT functions was demonstrated by means of biochemical studies ( 9, 16, 27, 31).
![francotte lyon francotte lyon](https://c8.alamy.com/comp/KXX591/francotte-cole-architecture-KXX591.jpg)
β-Strands 12 and 13 (amino acids 227 to 235) form the primer grip domain responsible for maintaining the primer terminus in an orientation appropriate for nucleophilic attack on the incoming deoxynucleoside triphosphate ( 15, 16, 23). In p66, a β-sheet (composed of β-strands 12 to 15) located downstream of the polymerase active site is implicated in binding the nucleic acid duplex and its translocation ( 23). The p66 subunit is 560 amino acids in length and constitutes the active element of the enzyme ( 5) with polymerase and RNase H activities, while the p51 subunit is a 440-residue derivative of p66 without the RNase H segment.
![francotte lyon francotte lyon](http://www.aiolfi.com/wp-content/uploads/images_lots//3151/3151_3.jpg)
Mature reverse transcriptase (RT) is composed of the p66 and p51 subunits. Interestingly, when a truncated recombinant consisting only of gag-PR is expressed, maturation occurs only in a fraction of the resultant particles with a marked reduction in Pr55 gag processing ( 8, 33), suggesting that only full-length gag-pol allows normal particle maturation. Although expression of the internal structural proteins alone is sufficient for the formation of noninfectious particles ( 8, 34), the presence of Pr160 gag-pol is required in the virion for maturation, which is an event controlled by the pol-encoded protease (PR) ( 7, 11, 17, 24). Incorporation of Pr160 gag-pol into assembling particles is thought to be mediated through interactions of its N-terminal Gag domain with Pr55 gag ( 13, 28, 34, 35). Pr55 gag and Pr160 gag-pol are cotranslationally modified by N-terminal attachment of a myristate ( 3, 11, 25, 29) and transported to the cell membrane, where assembly and budding occur ( 13, 37). Synthesis of Pr160 gag-pol occurs by occasional ribosomal frameshifting into the overlapping Pol reading frame during translation of gag ( 14, 38). The enzymatic components of the virion, which are encoded by pol, are synthesized as components of the larger polyprotein precursor, Pr160 gag-pol, which contains both gag- and pol-encoded sequences ( 37). The internal structural proteins of the virion are encoded by gag and are synthesized in the form of the polyprotein precursor, Pr55 gag. During formation of human immunodeficiency virus type 1 (HIV-1), structural proteins, enzymes, envelope glycoproteins, and genomic viral RNA are coordinately assembled at the cell membrane.