Watanabe S, Yogo Y, Yoshiike K
J Virol. 1984 Jan;49(1):78-85. doi: 10.1128/JVI.49.1.78-85.1984.
A plaque morphology mutant (pm-522) of BK virus (BKV) with a small deletion at map unit 0.72 can readily transform rat 3Y1 cells, but wild-type BKV (wt-501) cannot. We examined the expression of the viral early functions in BKV (wt-501 or pm-522)-infected 3Y1 cells within a 2-week period after infection, before foci of transformed cells became detectable, to know how the difference between the two BKVs occurs. After a high-multiplicity infection, comparable amounts of free viral DNA (forms I and II) were found by Southern blotting analyses to persist in the nuclei of the cells infected with wt and pm BKVs. Whereas the proportion of T antigen-positive cells, as revealed by the indirect immunofluorescence method with complement, remained at a level of 60% in pm BKV infection, the level of T antigen-positive cells in wt BKV infection decreased from the initial 45% to 1% on day 9. The results obtained by the immunoprecipitation analyses of radiolabeled proteins from the infected cells were consistent with the immunofluorescence data. Viral early mRNA was detectable on day 2 and increased on day 9 in pm BKV infection, but in wt BKV infection, the low level of early mRNA detected on day 2 disappeared on day 9. Cell DNA synthesis and cell growth were enhanced more in pm BKV infection than in wt BKV infection. The low level of viral DNA synthesis that occurred in the infected rat cells was more prominent in pm BKV infection than in wt BKV infection. These data indicate that the expression of viral early functions continued much longer in pm BKV-infected rat cells than in wt BKV-infected rat cells, where the expression was probably repressed soon after infection. Continued T antigen production directed by the unintegrated viral genomes appears to be required for efficient transformation of rat cells by BKV.
BK病毒（BKV）的一个斑块形态突变体（pm - 522）在图谱单位0.72处有一个小缺失，它能够轻易地转化大鼠3Y1细胞，而野生型BKV（wt - 501）则不能。我们在感染后2周内，在转化细胞灶变得可检测之前，检测了BKV（wt - 501或pm - 522）感染的3Y1细胞中病毒早期功能的表达情况，以了解这两种BKV之间的差异是如何产生的。在高倍感染后，通过Southern印迹分析发现，野生型和pm型BKV感染的细胞中，相当数量的游离病毒DNA（I型和II型）持续存在于细胞核中。用补体间接免疫荧光法显示，在pm型BKV感染中，T抗原阳性细胞的比例保持在60%的水平，而在野生型BKV感染中，T抗原阳性细胞的水平从最初的45%在第9天降至1%。对感染细胞中放射性标记蛋白进行免疫沉淀分析得到的结果与免疫荧光数据一致。在pm型BKV感染中，病毒早期mRNA在第2天可检测到，并在第9天增加，但在野生型BKV感染中，第2天检测到的低水平早期mRNA在第9天消失。与野生型BKV感染相比，pm型BKV感染对细胞DNA合成和细胞生长的促进作用更强。在感染的大鼠细胞中发生的低水平病毒DNA合成，在pm型BKV感染中比在野生型BKV感染中更显著。这些数据表明，病毒早期功能在pm型BKV感染的大鼠细胞中的表达持续时间比在野生型BKV感染的大鼠细胞中长得多，在野生型BKV感染的大鼠细胞中，其表达可能在感染后不久就受到抑制。由未整合的病毒基因组指导的持续T抗原产生似乎是BKV有效转化大鼠细胞所必需的。
