Nuclear import of Avian Sarcoma Virus integrase is facilitated by host cell factors.
BACKGROUND
Integration of retroviral DNA into the host cell genome is an obligatory step in the virus life cycle. In previous reports we identified a sequence (amino acids 201-236) in the linker region between the catalytic core and C-terminal domains of the avian sarcoma virus (ASV) integrase protein that functions as a transferable nuclear localization signal (NLS) in mammalian cells. The sequence is distinct from all known NLSs but, like many, contains basic residues that are essential for activity.


RESULTS
Our present studies with digitonin-permeabilized HeLa cells show that nuclear import mediated by the NLS of ASV integrase is an active, saturable, and ATP-dependent process. As expected for transport through nuclear pore complexes, import is blocked by treatment of cells with wheat germ agglutinin. We also show that import of ASV integrase requires soluble cellular factors but does not depend on binding the classical adapter Importin-alpha. Results from competition studies indicate that ASV integrase relies on one or more of the soluble components that mediate transport of the linker histone H1.


CONCLUSIONS
These results are consistent with a role for ASV integrase and cytoplasmic cellular factors in the nuclear import of its viral DNA substrate, and lay the foundation for identification of host cell components that mediate this reaction.
Andrake
Mark D
MD
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111, USA. mark.andrake@fccc.edu
Sauter
Monica M
MM
Boland
Kim
K
Goldstein
Andrew D
AD
Hussein
Maryem
M
Skalka
Anna Marie
AM
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001358:Avian Sarcoma Viruses / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D054884:Host-Pathogen Interactions; D006801:Humans; D019426:Integrases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D012192:Retroviridae Infections / Q000378:metabolism* / Q000821:virology; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D006657:Histones; D019913:Nuclear Localization Signals; D014764:Viral Proteins; D019426:Integrases