title: Human immunodeficiency virus type 1 N-terminal capsid mutants containing cores with abnormally high levels of capsid protein and virtually no reverse transcriptase.
abstract: We previously described the phenotype associated with three alanine substitution mutations in conserved residues (Trp23, Phe40, and Asp51) in the N-terminal domain of human immunodeficiency virus type 1 capsid protein (CA). All of the mutants produce noninfectious virions that lack conical cores and, despite having a functional reverse transcriptase (RT), are unable to initiate reverse transcription in vivo. Here, we have focused on elucidating the mechanism by which these CA mutations disrupt virus infectivity. We also report that cyclophilin A packaging is severely reduced in W23A and F40A virions, even though these residues are distant from the cyclophilin A binding loop. To correlate loss of infectivity with a possible defect in an early event preceding reverse transcription, we modeled disassembly by generating viral cores from particles treated with mild nonionic detergent; cores were isolated by sedimentation in sucrose density gradients. In general, fractions containing mutant cores exhibited a normal protein profile. However, there were two striking differences from the wild-type pattern: mutant core fractions displayed a marked deficiency in RT protein and enzymatic activity (<5% of total RT in gradient fractions) and a substantial increase in the retention of CA. The high level of core-associated CA suggests that mutant cores may be unable to undergo proper disassembly. Thus, taken together with the almost complete absence of RT in mutant cores, these findings can account for the failure of the three CA mutants to synthesize viral DNA following virus entry into cells.
authors: Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Shixing
authors: S
authors: Tang
authors: Tsutomu
authors: T
authors: Murakami
authors: Naiqian
authors: N
authors: Cheng
authors: Alasdair C
authors: AC
authors: Steven
authors: Eric O
authors: EO
authors: Freed
authors: Judith G
authors: JG
authors: Levin
mesh_terms: D036022:Capsid Proteins / Q000235:genetics / Q000378:metabolism*; D004279:DNA, Viral / Q000096:biosynthesis; D054303:HIV Reverse Transcriptase / Q000378:metabolism*; D015497:HIV-1 / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D008561:Membrane Fusion; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D014758:Viral Core Proteins / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D036022:Capsid Proteins; D004279:DNA, Viral; D014758:Viral Core Proteins; D054303:HIV Reverse Transcriptase