Ishii N, Nakanishi A, Yamada M, Macalalad M H, Kasamatsu H
Department of Biology, University of California, Los Angeles 90024.
J Virol. 1994 Dec;68(12):8209-16. doi: 10.1128/JVI.68.12.8209-8216.1994.
Structural proteins of simian virus 40 (SV40), Vp2 and Vp3 (Vp2/3) and Vp1, carry individual nuclear targeting signals, Vp3(198-206) (Vp2(316-324) and Vp1(1-8), respectively, which are encoded in different reading frames of an overlapping region of the genome. How signals coordinate nuclear targeting during virion morphogenesis was examined by using SV40 variants in which there is only one structural gene for Vp1 or Vp2/3, nuclear targeting-defective mutants thereof, Vp2/3(202T) and Vp1 delta N5, or nonoverlapping SV40 variants in which the genes for Vp1 and Vp2/3 are separated, and mutant derivatives of the gene carrying either one or both mutations. Nuclear targeting was assessed immunocytochemically following nuclear microinjection of the variant DNAs. When Vp2/3 and Vp1 mutants with defects in the nuclear targeting signals were expressed individually, the mutant proteins localized mostly to the cytoplasm. However, when mutant Vp2/3(202T) was coexpressed in the same cell along with wild-type Vp1, the mutant protein was effectively targeted to the nucleus. Likewise, the Vp1 delta N5 mutant protein was transported into the nucleus when wild-type Vp2/3 was expressed in the same cells. These results suggest that while Vp1 and Vp2/3 have independent nuclear targeting signals, additional signals, such as those defining protein-protein interactions, play a concerted role in nuclear localization along with the nuclear targeting signals of the individual proteins.
猴病毒40（SV40）的结构蛋白Vp2和Vp3（Vp2/3）以及Vp1带有各自的核定位信号，分别为Vp3（198 - 206）、Vp2（316 - 324）和Vp1（1 - 8），它们由基因组重叠区域的不同阅读框编码。通过使用仅含有一个Vp1或Vp2/3结构基因的SV40变体、其核定位缺陷突变体Vp2/3（202T）和Vp1 delta N5，或Vp1和Vp2/3基因分离的非重叠SV40变体以及携带一个或两个突变的基因的突变衍生物，研究了在病毒体形态发生过程中这些信号如何协调核定位。在对变体DNA进行核显微注射后，通过免疫细胞化学方法评估核定位。当单独表达具有核定位信号缺陷的Vp2/3和Vp1突变体时，突变蛋白大多定位于细胞质。然而，当突变体Vp2/3（202T）与野生型Vp1在同一细胞中共表达时，突变蛋白有效地靶向到细胞核。同样，当野生型Vp2/3在同一细胞中表达时，Vp1 delta N5突变蛋白被转运到细胞核中。这些结果表明，虽然Vp1和Vp2/3具有独立的核定位信号，但诸如定义蛋白质 - 蛋白质相互作用的那些额外信号，与单个蛋白质的核定位信号一起在核定位中发挥协同作用。
