Fuller M T, King J
Biophys J. 1980 Oct;32(1):381-401. doi: 10.1016/S0006-3495(80)84963-0.
In the morphogenesis of double stranded DNA phages, a precursor protein shell empty of DNA is first assembled and then filled with DNA. The assembly of the correctly dimensioned precursor shell (procapsid) of Salmonella bacteriophage P22 requires the interaction of some 420 coat protein subunits with approximately 200 scaffolding protein subunits to form a double shelled particle with the scaffolding protein on the inside. In the course of DNA packaging, all of the scaffolding protein subunits exit from the procapsid and participate in further rounds of procapsid assembly (King and Casjens. 1974. Nature (Lond.). 251:112-119). To study the mechanism of shell assembly we have purified the coat and scaffolding protein subunits by selective dissociation of isolated procapsids. Both proteins can be obtained as soluble subunits in Tris buffer at near neutral pH. The coat protein sedimented in sucrose gradients as a roughly spherical monomer, while the scaffolding protein sedimented as if it were an elongated monomer. When the two proteins were mixed together in 1.5 M guanidine hydrochloride and dialyzed back to buffer at room temperature, procapsids formed which were very similar in morphology, sedimentation behavior, and protein composition to procapsids formed in vivo. Incubation of either protein alone under the same conditions did not yield any large structures. We interpret these results to mean that the assembly of the shell involves a switching of both proteins from their nonaggregating to their aggregating forms through their mutual interaction. The results are discussed in terms of the general problem of self-regulated assembly and the control of protein polymerization in morphogenesis.
在双链DNA噬菌体的形态发生过程中，首先组装不含DNA的前体蛋白外壳，然后装入DNA。沙门氏菌噬菌体P22正确尺寸的前体外壳（原衣壳）的组装需要约420个衣壳蛋白亚基与约200个支架蛋白亚基相互作用，形成一个内部有支架蛋白的双层颗粒。在DNA包装过程中，所有支架蛋白亚基都从原衣壳中退出，并参与原衣壳的进一步组装轮次（金和卡斯延斯，1974年，《自然》（伦敦），251:112 - 119）。为了研究外壳组装机制，我们通过分离原衣壳的选择性解离来纯化衣壳蛋白和支架蛋白亚基。两种蛋白都可以在接近中性pH的Tris缓冲液中作为可溶性亚基获得。衣壳蛋白在蔗糖梯度中以大致球形的单体形式沉降，而支架蛋白沉降时好像是一个细长的单体。当两种蛋白在1.5 M盐酸胍中混合并在室温下透析回缓冲液时，形成的原衣壳在形态、沉降行为和蛋白质组成上与体内形成的原衣壳非常相似。在相同条件下单独孵育任何一种蛋白都不会产生任何大的结构。我们将这些结果解释为意味着外壳的组装涉及两种蛋白通过相互作用从非聚集形式转变为聚集形式。将根据自我调节组装的一般问题和形态发生中蛋白质聚合的控制来讨论这些结果。
