Lee S H, Kanda P, Kennedy R C, Walker J R
Department of Microbiology, University of Texas, Austin 78712.
Nucleic Acids Res. 1987 Oct 12;15(19):7663-75. doi: 10.1093/nar/15.19.7663.
The Escherichia coli DNA polymerase III holoenzyme 71.1 kDa tau subunit is a 643 amino acid protein encoded by the dnaX gene. This gene also encodes the holoenzyme 56.5 kDa gamma subunit. The tau factor (as a tau'-LacZ' fusion protein) has been isolated and shown to be cleaved in vitro to form gamma and a 135 kda C-terminal cleavage product. The tau'-LacZ' fusion protein, gamma, and the C-terminal cleavage product have been isolated. N-terminal sequencing has demonstrated that tau and gamma share the same N-terminal sequences and that tau is proteolytically cleaved in vitro between residues 498 and 499 to form gamma. In addition, residues 420-440 were shown to be present in both tau and gamma by use of antibody specific for a synthetic peptide corresponding to that sequence. Some mechanism functions in vivo to ensure that tau and gamma are synthesized in a ratio of about one-to-one, as shown by radioimmune precipitation of tau and gamma from cellular extracts.
大肠杆菌DNA聚合酶III全酶的71.1 kDa τ亚基是一种由dnaX基因编码的643个氨基酸的蛋白质。该基因还编码全酶的56.5 kDa γ亚基。τ因子（作为τ'-LacZ'融合蛋白）已被分离出来，并显示在体外被切割形成γ和一个135 kDa的C端切割产物。已分离出τ'-LacZ'融合蛋白、γ和C端切割产物。N端测序表明，τ和γ共享相同的N端序列，并且τ在体外498和499位残基之间被蛋白水解切割形成γ。此外，通过使用针对对应于该序列的合成肽的特异性抗体，表明420 - 440位残基同时存在于τ和γ中。体内存在某种机制以确保τ和γ以大约一对一的比例合成，这从细胞提取物中τ和γ的放射免疫沉淀结果可以看出。
