Vytvytska O, Jakobsen J S, Balcunaite G, Andersen J S, Baccarini M, von Gabain A
Institute of Microbiology and Genetics, Vienna Biocenter, University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14118-23. doi: 10.1073/pnas.95.24.14118.
The stability of the ompA mRNA depends on the bacterial growth rate. The 5' untranslated region is the stability determinant of this transcript and the target of the endoribonuclease, RNase E, the key player of mRNA degradation. An RNA-binding protein with affinity for the 5' untranslated region ompA was purified and identified as Hfq, a host factor initially recognized for its function in phage Qbeta replication. The ompA RNA-binding activity parallels the amount of Hfq, which is elevated in bacteria cultured at slow growth rate, a condition leading to facilitated degradation of the ompA mRNA. In hfq mutant cells with a deficient Hfq gene product, the RNA-binding activity is missing, and analysis of the ompA mRNA showed that the growth-rate dependence of degradation is lost. Furthermore, the half-life of the ompA mRNA is prolonged in the mutant cells, irrespective of growth rate. Hfq has no affinity for the lpp transcript whose degradation, like that of bulk mRNA, is not affected by bacterial growth rate. Compatible with our results, we found that the intracellular concentration of RNase E and its associated degradosome components is independent of bacterial growth rate. Thus our results suggest a regulatory role for Hfq that specifically facilitates the ompA mRNA degradation in a growth rate-dependent manner.
ompA mRNA的稳定性取决于细菌的生长速率。5'非翻译区是该转录本的稳定性决定因素，也是核糖核酸内切酶RNase E的作用靶点，RNase E是mRNA降解的关键参与者。一种对ompA的5'非翻译区具有亲和力的RNA结合蛋白被纯化并鉴定为Hfq，它是一种宿主因子，最初因其在噬菌体Qβ复制中的功能而被识别。ompA的RNA结合活性与Hfq的量平行，Hfq在生长缓慢的细菌培养物中含量升高，这种条件会导致ompA mRNA的降解加快。在Hfq基因产物缺陷的hfq突变细胞中，RNA结合活性缺失，对ompA mRNA的分析表明其降解对生长速率的依赖性丧失。此外，无论生长速率如何，ompA mRNA在突变细胞中的半衰期都会延长。Hfq对lpp转录本没有亲和力，lpp转录本的降解与大量mRNA的降解一样，不受细菌生长速率的影响。与我们的结果一致，我们发现RNase E及其相关降解体成分的细胞内浓度与细菌生长速率无关。因此，我们的结果表明Hfq具有一种调节作用，即以生长速率依赖性方式特异性促进ompA mRNA的降解。
