Bazinet C, Benbasat J, King J, Carazo J M, Carrascosa J L
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Biochemistry. 1988 Mar 22;27(6):1849-56. doi: 10.1021/bi00406a009.
The gene 1 protein of Salmonella bacteriophage P22 is located at the DNA packaging vertex of the mature particle. The protein is incorporated into the procapsid shell during shell assembly and is required for DNA packaging. The unassembled precursor form of the gene 1 protein has been purified from cells infected with mutants blocked in procapsid assembly. The purified 90,000-dalton protein was dimeric or monomeric; upon storage in the cold it formed 20S cyclic dodecamers. Computer filtering of negatively stained electron micrographs revealed 12 arms and knobs projecting from a central ring, with a 30-A channel at the center. Similar dodecameric rings were released from disrupted procapsid shells. These results indicate that the gene 1 protein is organized as a cyclic dodecamer within the procapsid shell and serves as the portal through which P22 DNA is threaded during DNA packaging. The presence of a 12-fold ring located at a 5-fold portal vertex appears to be a conserved structural theme of the DNA packaging apparatus of double-stranded DNA phages.
沙门氏菌噬菌体P22的基因1蛋白位于成熟噬菌体颗粒的DNA包装顶点。该蛋白在衣壳组装过程中被整合到原衣壳中，是DNA包装所必需的。基因1蛋白未组装的前体形式已从感染了在原衣壳组装中受阻的突变体的细胞中纯化出来。纯化的90,000道尔顿蛋白为二聚体或单体；在低温下储存时，它会形成20S环状十二聚体。对负染电子显微镜照片进行计算机过滤后发现，有12个臂和旋钮从一个中心环伸出，中心有一个30埃的通道。从破裂的原衣壳中也释放出了类似的十二聚体环。这些结果表明，基因1蛋白在原衣壳内组装成环状十二聚体，并作为P22 DNA在包装过程中穿过的通道。位于5倍对称的门户顶点的12倍对称环的存在似乎是双链DNA噬菌体DNA包装装置的一个保守结构特征。
