Sfakianos Jeffrey N, LaCasse Rachel A, Hunter Eric
Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Traffic. 2003 Oct;4(10):660-70. doi: 10.1034/j.1600-0854.2003.00125.x.
Intracytoplasmic protein targeting in mammalian cells is critical for organelle function as well as virus assembly, but the signals that mediate it are poorly defined. We show here that Mason-Pfizer monkey virus specifically targets Gag precursor proteins to the pericentriolar region of the cytoplasm in a microtubule dependent process through interactions between a short peptide signal, known as the cytoplasmic targeting-retention signal, and the dynein/dynactin motor complex. The Gag molecules are concentrated in pericentriolar microdomains, where they assemble to form immature capsids. Depletion of Gag from this region by cycloheximide treatment, coupled with the presence of ribosomal clusters that are in close vicinity to the assembling capsids, suggests that the dominant N-terminal cytoplasmic targeting-retention signal functions in a cotranslational manner. Transport of the capsids out of the pericentriolar assembly site requires the env-gene product, and a functional vesicular transport system. A single point mutation that renders the cytoplasmic targeting-retention signal defective abrogates pericentriolar targeting of Gag molecules. Thus the previously defined cytoplasmic targeting-retention signal appears to act as a cotranslational intracellular targeting signal that concentrates Gag proteins at the centriole for assembly of capsids.
在哺乳动物细胞中，胞质内蛋白质靶向对于细胞器功能以及病毒组装至关重要，但介导这一过程的信号却鲜为人知。我们在此表明，梅森- Pfizer猴病毒通过一种短肽信号（称为胞质靶向-保留信号）与动力蛋白/动力蛋白激活蛋白复合物之间的相互作用，以微管依赖的方式将Gag前体蛋白特异性靶向到细胞质的中心粒周围区域。Gag分子集中在中心粒周围的微结构域中，在那里它们组装形成未成熟的衣壳。通过环己酰亚胺处理从该区域耗尽Gag，再加上与正在组装的衣壳紧邻的核糖体簇的存在，表明主要的N端胞质靶向-保留信号以共翻译的方式发挥作用。衣壳从中心粒周围组装位点的运输需要env基因产物和一个功能性的囊泡运输系统。使胞质靶向-保留信号有缺陷的单点突变消除了Gag分子的中心粒周围靶向。因此，先前定义的胞质靶向-保留信号似乎充当了一种共翻译的细胞内靶向信号，将Gag蛋白集中在中心粒处以组装衣壳。
