ESCHERICHIA-COLI SINGLE-STRAND BINDING-PROTEIN ORGANIZES SINGLE-STRANDED-DNA IN NUCLEOSOME-LIKE UNITS
ESCHERICHIA-COLI SINGLE-STRAND BINDING-PROTEIN ORGANIZES SINGLE-STRANDED-DNA IN NUCLEOSOME-LIKE UNITS
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DOI：
10.1073/pnas.79.19.5803
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发表时间：
1982-01-01
期刊：
影响因子：
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通讯作者：
GRIFFITH, J
中科院分区：
文献类型：
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作者：
CHRYSOGELOS, S;GRIFFITH, J
电镜观察表明，E.大肠杆菌和噬菌体fd DNA表现为珠状纤维环，平均含有38个珠，每170个DNA碱基中有1个珠。用微球菌核酸酶对天然未固定的SSB-fd DNA复合物的广泛消化揭示了145个碱基的受保护的DNA片段，而较短的消化时间导致160 ± 1的倍数的片段序列。25个基地用DNA酶I消化这些复合物产生重复的条带模式，约15个碱基的倍数，在60、105、118、130、145、150和210个碱基处具有强条带。在CsCl溶液中的等密度带分别产生密度为1.272和1.700 g/ml，对于单独的SSB和对于fd DNA，固定后，对于fd DNA-SSB珠状纤维为1.388 g/ml，对于单个蛋白质-DNA珠为1.373 g/ml。根据这些数据和SSB和fd DNA的分子量，我们认为核蛋白链由8个SSB分子与145个DNA碱基结合组成，这些单元由大约30个无蛋白质DNA碱基连接。通过酶消化未固定的天然样品，并在固定后，通过EM和密度带得到的结果之间的极好的一致性支持的结论，SSB组织单链DNA的方式类似于双链体DNA的组织由组蛋白。
EM shows that complexes of the single-strand DNA binding protein (SSB) of E. coli and phage fd DNA appear as beaded fiber loops containing an average of 38 beads, 1 per 170 bases of DNA. Extensive digestion of native unfixed SSB-fd DNA complexes with micrococcal nuclease reveals a protected DNA fragment of 145 bases, while shorter digestion periods result in a sequence of fragments in multiples of 160 .+-. 25 bases. Digestion of these complexes with DNase I produces a repeating pattern of bands, multiples of approximately 15 bases with strong bands at 60, 105, 118, 130, 145, 150 and 210 bases. Isopycnic banding in CsCl solution yields densities of 1.272 and 1.700 g/ml, respectively, for SSB alone and for fd DNA and, after fixation, of 1.388 g/ml for fd DNA-SSB beaded fibers and 1.373 g/ml for the individual protein-DNA beads. Based on these data and the MW of SSB and fd DNA, it is suggested that the nucleoprotein chain consists of 8 molecules of SSB bound to 145 bases of DNA, with these units linked by roughly 30 bases of protein-free DNA. The excellent concord between results obtained by enzyme digestion of unfixed native samples and, after fixation, by EM and density banding supports the conclusion that SSB organizes single-stranded DNA in a manner similar to the organization of duplex DNA by histones.