RT and IN were detected with anti-RT and anti-IN serum

RT and IN were detected with anti-RT and anti-IN serum. suggesting that Naringenin in addition to contributing to RT biological function during the early stages of virus replication, the HIV-1 RT tryptophan repeat motif in a Gag-Pol context may play an important role in suppressing the premature activation of PR during late-stage virus replication. In the late stage of human immunodeficiency virus type 1 (HIV-1) replication, thousands of viral capsid precursor (Pr55gag) molecules assemble into virus particles and bud out from the plasma membrane (42). During or soon after virus budding, Pr55gagis cleaved by viral protease (PR) into four major products: matrix (MA) (p17), capsid (CA) (p24), nucleocapsid (NC) (p7), and the C-terminal p6 domain (42). PR is encoded bypol, which is initially translated as the polyprotein Naringenin precursor Pr160gag-pol. It is Naringenin generally believed that Pr160gag-polis incorporated into assembling virions via interaction with Pr55gagthrough its N-terminal Gag determinants Rabbit polyclonal to NPSR1 (10,11,19,22,40,41). However, some researchers have demonstrated that HIV-1 and murine leukemia virus (MLV) Pol can be packaged into virions at a reasonable efficiency despite an absence of Gag-Pol formation (3,7). The proteolytic processing of Pr160gag-polgives rise to PR, reverse transcriptase (RT), Naringenin and integrase (IN) in addition to Gag cleavage products. Blocking PR activity does not significantly affect virus particle assembly and release, but it does eliminate viral infectivity (17,27,36). The reading frame of HIV-1polpartially overlaps that ofgag. During Gag translation, a 1 ribosomal frameshift event occurs at a frequency of 5%, resulting in an approximately 1:20 expression level of Pr160gag-polto Pr55gag(24). An artificial overexpression of Pr160gag-polor PR-containing chimeric proteins results in a Naringenin significant reduction in virion release, presumably due to the premature cleavage of Pr55gagas mediated by PR (1,20,28,35,38,39,48). Accordingly, both the PR expression level and PR activation timing with respect to the proteolytic processing of Gag and Gag-Pol are critical to virus assembly. The molecular mechanism behind PR activation is not entirely clear. It is generally accepted that Pr160gag-poldimerization or multimerization triggers PR activation, and therefore, sequences upstream or downstream of PR may affect PR-mediated virus maturation by interfering with Gag-Pol multimerization. Consistent with this suggestion, deletions of sequences upstream of PR (11,52) or mutations in downstreampolsequences can significantly affect PR-directed virus particle maturation (4,30,37). Biologically active RT is assumed to be present in the form of a p66/p51 heterodimer (12,31). A hydrophobic cluster consisting of six tryptophan (Trp) residues has been identified in the connection subdomain of the HIV-1 RT subunit (codons 398 to 414). This Trp repeat motif is highly conserved among primate lentiviral reverse transcriptases (2). It has been shown that substitution mutations of HIV-1 RT Trp repeat motif residues can markedly impair RT dimerization in vitro (33,44), suggesting a motif role in RT-RT interactions. Although the extent to which the RT domain contributes to Gag-Pol multimerization is unknown, some data support the idea that the RT sequence (the Trp repeat motif in particular) may affect PR activation by favoring Gag-Pol multimerization. First, RT truncation mutations involving the Trp repeat motif significantly impair PR-mediated Gag processing (30). Second, efavirenz (EFV)a nonnucleoside reverse transcriptase inhibitor (NNRTI) that greatly enhances HIV-1 RT dimerization in vitro (46,47)is capable of suppressing virion production by enhancing the efficiency of PR-mediated Gag and Gag-Pol cleavage (14,45). However, a W401A alanine substitution mutation that abrogates RT dimerization in vitro (49) almost completely negates the EFV inhibitory effect on virion production (9). The lack of W401A susceptibility to this inhibitory effect is most likely due to.