Chattoraj D, Cordes K, Abeles A
Proc Natl Acad Sci U S A. 1984 Oct;81(20):6456-60. doi: 10.1073/pnas.81.20.6456.
The incompatibility locus, incA, of the unit-copy plasmid P1 is contained within a fragment that is essentially a set of nine 19-base-pair repeats. One or more copies of the fragment destabilizes the plasmid when present in trans. Here we show that extra copies of incA interfere with plasmid DNA replication and that a deletion of most of incA increases plasmid copy number. Thus, incA is not essential for replication but is required for its control. When cloned in a high-copy-number vector, pieces of the incA fragment that each contain only three repeats destabilize P1 plasmids efficiently. This result makes it unlikely that incA specifies a regulatory product. Our in vivo results suggest that the repeating DNA sequence itself negatively controls replication by titrating a P1-determined protein, RepA, that is essential for replication. Consistent with this hypothesis is the observation that the RepA protein binds to the incA fragment in vitro.
单位拷贝质粒P1的不相容性基因座incA包含在一个片段内，该片段本质上是一组9个19碱基对的重复序列。当该片段的一个或多个拷贝以反式存在时，会使质粒不稳定。我们在此表明，incA的额外拷贝会干扰质粒DNA复制，而大部分incA的缺失会增加质粒拷贝数。因此，incA对于复制不是必需的，但对其控制是必需的。当克隆到高拷贝数载体中时，每个仅包含三个重复序列的incA片段能有效地使P1质粒不稳定。这一结果表明incA不太可能指定一种调节产物。我们的体内实验结果表明，重复DNA序列本身通过滴定一种对复制至关重要的由P1决定的蛋白质RepA来负向控制复制。与这一假设一致的是，观察到RepA蛋白在体外与incA片段结合。
