Abeles A L, Friedman S A, Austin S J
J Mol Biol. 1985 Sep 20;185(2):261-72. doi: 10.1016/0022-2836(85)90402-4.
The boundaries of the P1 par (plasmid partition) region of the unit-copy plasmid P1 were defined to within 2.7 X 10(3) base-pairs of DNA. The DNA sequence of the region revealed two large open reading frames that could encode proteins of Mr 44,000 and Mr 38,000. Both would be read in the same direction. The first open reading frame corresponds to the par A gene, the Mr 44,000 protein product of which was shown to be trans acting and essential for partition. The second open reading frame (parB) follows closely and may be cotranscribed with par A. The codon usage frequency for parB is consistent with its producing a protein product. The ParB protein was identified in cell extracts as a product with an apparent Mr of 45,000, suggesting that it behaves anomolously on gel electrophoresis. Following parB is the incB region, an incompatibility determinant thought to be the cis acting site that constitutes the putative attachment point on the DNA for the cellular partition apparatus. Subcloning of this site showed it to consist of a maximum of 174 base-pairs. The incB sequence is highly A + T-rich and contains a 20 base-pair inverted repeat. Another A + T-rich inverted repeat of similar size but different sequence is found between the putative parA promoter and the ribosome initiation sequence at the start of the parA open reading frame and may be involved in the autoregulation of ParA synthesis. The par region appears to contain a functional analog of the centromere of eukaryotic chromosomes. It is responsible for ensuring that newly replicated plasmids are properly distributed to daughter cells during cell division of its Escherichia coli host.
单位拷贝质粒P1的P1 par（质粒分配）区域的边界被确定在2.7×10³个碱基对的DNA范围内。该区域的DNA序列揭示了两个大的开放阅读框，它们可能编码分子量为44,000和38,000的蛋白质。两者都将按相同方向阅读。第一个开放阅读框对应于parA基因，其分子量为44,000的蛋白质产物被证明具有反式作用且对分配至关重要。第二个开放阅读框（parB）紧随其后，可能与parA共转录。parB的密码子使用频率与其产生蛋白质产物一致。在细胞提取物中鉴定出ParB蛋白是一种表观分子量为45,000的产物，这表明它在凝胶电泳中表现异常。parB之后是incB区域，一个不相容性决定簇，被认为是顺式作用位点，构成了细胞分配装置在DNA上的假定附着点。该位点的亚克隆显示它最多由174个碱基对组成。incB序列富含A+T，包含一个20个碱基对的反向重复序列。在假定的parA启动子和parA开放阅读框起始处的核糖体起始序列之间发现了另一个大小相似但序列不同的富含A+T的反向重复序列，它可能参与ParA合成的自动调节。par区域似乎包含真核染色体着丝粒的功能类似物。它负责确保新复制的质粒在其大肠杆菌宿主细胞分裂期间正确地分配到子细胞中。
