A nucleoprotein complex mediates the integration of retroviral DNA.

Abstract

The integration of viral DNA into the host genome is an essential step in the retrovirus life cycle. To understand this process better, we have examined the native state of viral DNA in cells acutely infected by murine leukemia virus (MLV), using both a physical assay for viral DNA and a functional assay for integration activity (Brown et al. 1987). The viral DNA and integration activity copurify during velocity sedimentation, gel filtration, and density equilibrium centrifugation, indicating that viral DNA is in a large (-160S) nucleoprotein complex that includes all functions required for integration activity in vitro. Analysis by immunoprecipitation shows that the viral capsid protein is part of the active nucleoprotein complex, but recognition of the complex by only a subset of anti-capsid sera implies that the protein is constrained conformationally. The viral DNA within this structure is accessible to nucleases; the effects of nucleases on the integrity of the complex suggest that the integration-competent particle is derived from and similar to the core of extracellular virions.

Integrase, LEDGF/p75 and HIV replication

“…The PIC is a macromolecular assemblage that consists of the viral cDNA, a subset of viral proteins retained from the initial reverse transcription complex, and probably host cell proteins [5,[15][16][17][18][19]. Similarly, chromatin is compositionally and structurally intricate.…”

The Gag polypeptides of the Drosophila 1731 retrotransposon are associated to virus‐like particles and to nuclei

“…We can now propose that this direction to the nucleus could be monitored by a NLS-like sequence (nucleotide position: 1079 to 1102 in the cDm2055 plasmid -see [36]); this sequence is found close to the nucleic acid binding site (nucleotide position 1123 to 1165 ), suggesting similar structural organisations in the Gag products of both copia and 1731. It has also been reported that the Gag product of Moloney Leukemia Virus was associated with the nucleoprotein complex involved in the process of transposition [37]. In addition the localization of Gag protein of foamy viruses was found to be nuclear, a localization due to the presence of glycine-arginine rich boxes (NLS-like) in its sequence [14].…”

Early Detection of a Two-Long-Terminal-Repeat Junction Molecule in the Cytoplasm of Recombinant Murine Leukemia Virus-Infected Cells

“…The mechanism by which the MLV PIC enters the nucleus remains unclear, and the requirement for mitosis for MLV but not for human immunodeficiency virus (HIV) nuclear import was supposed to be simply due to the large size of the MLV nucleoprotein complex (2,16). Nevertheless, neither the MLV nor the HIV PIC enters the nucleus by passive transport.…”

“…Reverse transcription (RT) occurs in an intracellular complex made of cellular and viral proteins termed the preintegration complex (PIC) (2). During and after mitosis, the PIC penetrates the nuclear compartment and the viral DNA integrates, as recently shown, into the human host cell genome near the start of transcriptional units (48).…”

“…However, sequence analysis of the host cell genome-provirus junctions was somewhat heterogeneous. Linear DNA was described as the precursor of integration since the murine leukemia virus (MLV) PIC isolated from the cytoplasm of infected cells and containing the linear forms of viral DNA was competent to carry out integration in vitro (2,4).…”