Menéndez-Arias L, Risco C, Pinto da Silva P, Oroszlan S
Laboratory of Molecular Virology and Carcinogenesis, NCI-Frederick Cancer Research and Development Center, Maryland 21702-1201.
J Virol. 1992 Sep;66(9):5615-20. doi: 10.1128/JVI.66.9.5615-5620.1992.
The immature capsids of the mouse mammary tumor virus (MMTV), known as intracytoplasmic A particles, have been isolated from murine L1210 leukemia cells. The diameter of the isolated particles was 80 nm as determined by negative staining. Two polypeptides of 77 and 110 kDa were found to be their major polypeptide components, in agreement with the expected sizes of the Gag and Gag-Pro precursor polypeptides of the mature MMTV proteins. Both polypeptides were recognized by antibodies directed toward the matrix (p10) and capsid (p27) proteins of MMTV. Immunogold labeling of p10 on isolated A particles, visualized by negative staining, showed that this protein is located at the surface of the immature capsids, whereas p27 can be detected only in broken or disrupted particles, suggesting that it has an internal location. These observations were confirmed by immunolabeling of both proteins on thin sections of A particle-producing cells. In addition, the viral protease had a more internal position than p27. Since the sequential order of the viral proteins in the Gag precursor is p10-pp21-p27-p14 and that in Gag-Pro is p10-pp21-p27-p30-protease, our results demonstrate the radial organization of the polypeptide precursors forming the intracytoplasmic A particles.
小鼠乳腺肿瘤病毒（MMTV）的未成熟衣壳，即胞质A型颗粒，已从鼠L1210白血病细胞中分离出来。通过负染法测定，分离出的颗粒直径为80纳米。发现两种分子量分别为77 kDa和110 kDa的多肽是其主要多肽成分，这与成熟MMTV蛋白的Gag和Gag-Pro前体多肽的预期大小一致。这两种多肽都能被针对MMTV基质（p10）和衣壳（p27）蛋白的抗体识别。通过负染法观察到，分离出的A型颗粒上p10的免疫金标记显示该蛋白位于未成熟衣壳的表面，而p27仅在破碎或破坏的颗粒中才能检测到，这表明它位于内部。在产生A型颗粒的细胞的超薄切片上对这两种蛋白进行免疫标记，证实了这些观察结果。此外，病毒蛋白酶的位置比p27更靠内部。由于Gag前体中病毒蛋白的顺序是p10-pp21-p27-p14，而Gag-Pro中的顺序是p10-pp21-p27-p30-蛋白酶，我们的结果证明了形成胞质A型颗粒的多肽前体的径向组织。
