Shinger V, Thomas C M
Mol Gen Genet. 1984;195(3):523-9. doi: 10.1007/BF00341457.
Transcription at various points in the trf A region of broad host range plasmid RK2 has been analysed by measuring expression of the galK gene inserted at EcoRI sites introduced previously by TB1723 transposition mutagenesis. Rightward transcription (anti-clockwise on RK2) probably from a single promoter, proceeds across two open reading frames coding for a 13 kD polypeptide of unknown function, and the trf A gene, which provides a protein(s) essential for plasmid replication. This transcription is not auto-regulated by the products of either open reading frame and is also not subject to significant attenuation prior to the end of the trfA open reading frame. Leftward transcription appears to be directed by at least two well separated promoters, the more leftward being three to four times stronger than the more rightward. Rightward, but not leftward, transcription is repressed about 9-fold by the trfB locus of RK2 alone (so far not separable from the loci korA and korD) in trans while the combination of the korB and trfB loci in trans represses both rightward transcription (about 100-fold) and leftward transcription (the stronger activity by 10 to 15-fold). Regulation of these operons is therefore qualitatively different. The kilD locus in the trfA region, which is suppressed by korD (trfB) is thus probably part of the rightward (trfA) operon, while leftward transcription may represent the start of an operon containing kilB. The results suggest that RK2kor loci act by repressing transcription of kil loci and that the kil and kor control circuits may be part of an interlocking system of RK2 genes involved in replication and stable maintenance.
通过测量经TB1723转座诱变先前引入的EcoRI位点处插入的galK基因的表达，分析了广宿主范围质粒RK2的trfA区域不同位点的转录情况。向右转录（在RK2上为逆时针方向）可能来自单个启动子，穿过两个开放阅读框，这两个开放阅读框编码一种功能未知的13kD多肽以及trfA基因，trfA基因提供质粒复制所必需的一种或多种蛋白质。这种转录不受任何一个开放阅读框产物的自动调节，并且在trfA开放阅读框末端之前也没有明显的衰减。向左转录似乎由至少两个相距较远的启动子指导，较左边的启动子比右边的强三到四倍。单独的RK2的trfB位点（目前与korA和korD位点不可分离）反式作用时，可使向右但不使向左转录受到约9倍的抑制，而反式作用的korB和trfB位点组合则同时抑制向右转录（约100倍）和向左转录（较强活性的转录被抑制10到15倍）。因此，这些操纵子的调控在性质上是不同的。trfA区域中被korD（trfB）抑制的kilD位点可能因此是向右（trfA）操纵子的一部分，而向左转录可能代表包含kilB的操纵子的起始。结果表明，RK2 kor位点通过抑制kil位点的转录起作用，并且kil和kor控制电路可能是参与复制和稳定维持的RK2基因互锁系统的一部分。
