Molecular dissection of nuclear entry-competent SV40 during infection.
To establish viral infection, SV40 must expose nuclear localization signals (NLSs) that are internal in the virion architecture in order to enter the nucleus via interaction with the host's nuclear import machinery, which includes importin alpha and importin beta. The time course for SV40 association with the importins in infected cells was examined. The viral DNA associated with importin alpha by 1.5h post infection, before associating with the importin beta nuclear import receptor, by 3h post infection. Only a small fraction of cell-internalized SV40 that contained viral DNA was bound by the two importins. This fraction, termed "nuclear entry-competent SV40," was slightly smaller than the virion but, importantly, was larger than the viral chromatin and contained both Vp1 and Vp3. Furthermore, the internalized viral DNA in either anti-importin or anti-Vp3 immune complexes was sensitive to DNase I, whereas the viral DNA in mature virions was resistant. All these results suggest that once SV40 enters the cytoplasm, it undergoes an architectural modification that exposes the virion's NLSs for nuclear entry.
Nakanishi
Akira
A
Department of Molecular, Cell, and Developmental Biology and Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
Li
Peggy P
PP
Qu
Qiumin
Q
Jafri
Qumber H
QH
Kasamatsu
Harumi
H
D000818:Animals; D036022:Capsid Proteins / Q000032:analysis; D002460:Cell Line; D004279:DNA, Viral / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D000882:Haplorhini; D007700:Kinetics; D046911:Macromolecular Substances / Q000378:metabolism; D011485:Protein Binding; D013539:Simian virus 40 / Q000235:genetics* / Q000502:physiology*; D014764:Viral Proteins / Q000378:metabolism*; D028901:alpha Karyopherins / Q000378:metabolism*; D028961:beta Karyopherins / Q000378:metabolism*
D036022:Capsid Proteins; D004279:DNA, Viral; D046911:Macromolecular Substances; C062481:VP1 protein, polyomavirus; C085902:VP3 protein, Simian virus 40; D014764:Viral Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; D003850:Deoxyribonuclease I