Gerdes K, Thisted T, Martinussen J
Department of Molecular Biology, Odense University, Denmark.
Mol Microbiol. 1990 Nov;4(11):1807-18. doi: 10.1111/j.1365-2958.1990.tb02029.x.
The hok/sok system of plasmid R1, which mediates plasmid stabilization via killing of plasmid-free segregants, encodes two genes: hok and sok. The hok gene product is a potent cell-killing protein. The expression of hok is regulated post-transcriptionally by the sok gene-encoded repressor, an antisense RNA complementary to the hok mRNA leader region. We show here that the hok mRNA is very stable, while the sok RNA decays rapidly. We also observe a new hok mRNA species which is 70 nucleotides shorter in the 3'-end than the full-length hok transcript. The appearance of the truncated hok mRNA was found to be regulated by the sok antisense RNA. Furthermore, the presence of the truncated hok mRNA was found to be correlated with efficient expression of the Hok protein. On the basis of these findings, we propose an extended model in order to explain the killing of plasmid-free segregants by the hok/sok system.
质粒R1的hok/sok系统通过杀死不含质粒的分离菌来介导质粒稳定，该系统编码两个基因：hok和sok。hok基因产物是一种强效的细胞杀伤蛋白。hok的表达在转录后由sok基因编码的阻遏物调控，sok基因编码的阻遏物是一种与hok mRNA前导区互补的反义RNA。我们在此表明，hok mRNA非常稳定，而sok RNA迅速降解。我们还观察到一种新的hok mRNA物种，其3'端比全长hok转录本短70个核苷酸。发现截短的hok mRNA的出现受sok反义RNA调控。此外，发现截短的hok mRNA的存在与Hok蛋白的有效表达相关。基于这些发现，我们提出一个扩展模型以解释hok/sok系统对不含质粒的分离菌的杀伤作用。
