Rakonjac J, Model P
The Rockefeller University, 1230 York Avenue, New York, NY, 10021, USA.
J Mol Biol. 1998 Sep 11;282(1):25-41. doi: 10.1006/jmbi.1998.2006.
Filamentous phage protein III (pIII), located at one end of the phage, is required for infectivity and stability of the particle. Cells infected with phage from which gene III has been completely deleted produce particles that are not released into the medium but stay associated at the surface. These particles are much longer than normal phage. They can be released by subsequent expression of pIII. Viewed with the electron microscope, cells infected with gene III deletion phage are decorated with structures that resemble extremely long pili. Surprisingly, such cells are viable and can form colonies. The pIII deficiency can be complemented in trans, but there is a threshold concentration below which assembly does not occur. Above this threshold, pIII is used very efficiently and is incorporated into infectious but longer than unit length phage. As the concentration of pIII is increased, the number of infectious particles increases, and their average length decreases.pIII stabilizes pVI, a second phage protein found at the pIII end of the particle. In the absence of pIII, degradation of pVI is very rapid. pIII is thus not only required for infectivity and particle stability, but to terminate assembly and release the phage from its assembly site.
丝状噬菌体蛋白III（pIII）位于噬菌体的一端，是噬菌体感染性和颗粒稳定性所必需的。用已完全缺失基因III的噬菌体感染细胞，产生的颗粒不会释放到培养基中，而是留在细胞表面。这些颗粒比正常噬菌体长得多。它们可以通过随后表达pIII而释放。用电子显微镜观察，被基因III缺失噬菌体感染的细胞表面装饰着类似极长菌毛的结构。令人惊讶的是，这样的细胞是有活力的，并且能够形成菌落。pIII缺陷可以通过反式互补来弥补，但存在一个阈值浓度，低于该浓度组装就不会发生。高于这个阈值，pIII被非常有效地利用，并被整合到具有感染性但比单位长度更长的噬菌体中。随着pIII浓度的增加，感染性颗粒的数量增加，其平均长度减小。pIII稳定pVI，pVI是在颗粒的pIII端发现的第二种噬菌体蛋白。在没有pIII的情况下，pVI的降解非常迅速。因此，pIII不仅是感染性和颗粒稳定性所必需的，而且对于终止组装并将噬菌体从其组装位点释放也是必需的。
