Sandler P, Weisblum B
Department of Pharmacology, University of Wisconsin Medical School, Madison 53706.
J Bacteriol. 1989 Dec;171(12):6680-8. doi: 10.1128/jb.171.12.6680-6688.1989.
The Staphylococcus aureus ermA gene, whose product confers resistance to the macrolide-lincosamide-streptogramin B family of antibiotics, is induced at the level of translation by nanomolar concentrations of erythromycin. Erythromycin also specifically stabilizes ermA transcripts, and the induced stabilization requires in-phase translation of at least one of two small leader peptides in the 5' leader region of the transcript. Erythromycin-induced mRNA stabilization was tested in three constructions in which the ermA transcript was elongated by making insertions at the ermA transcription start. Whereas mRNA downstream of the leader peptide is stabilized by erythromycin, mRNA upstream is not. In the presence of erythromycin, specific mRNA decay intermediates in both the extended ermA genes and the wild-type ermA gene were detected by both Northern blotting and S1 nuclease mapping. The 5' ends of the intermediates map to the sequences that encode each of the two ermA leader peptides, suggesting that the intermediates are produced by stalled erythromycin-bound ribosomes acting as barricades to degradation by 5'-to-3' RNases. In addition, whereas erythromycin was found previously to stabilize ermA transcripts only physically, an ermC-cat-86 hybrid transcript was stabilized both physically and functionally by erythromycin.
金黄色葡萄球菌ermA基因的产物赋予对大环内酯-林可酰胺-链阳菌素B类抗生素的抗性，该基因在翻译水平上由纳摩尔浓度的红霉素诱导。红霉素还能特异性地稳定ermA转录本，且诱导的稳定性需要转录本5'前导区两个小前导肽中至少一个进行同框翻译。在三种构建体中测试了红霉素诱导的mRNA稳定性，在这些构建体中，通过在ermA转录起始位点进行插入来延长ermA转录本。虽然前导肽下游的mRNA被红霉素稳定，但上游的mRNA则不然。在红霉素存在的情况下，通过Northern印迹法和S1核酸酶作图法在延长的ermA基因和野生型ermA基因中均检测到特定的mRNA降解中间体。中间体的5'端定位于编码两个ermA前导肽中每一个的序列，这表明中间体是由结合红霉素的停滞核糖体产生的，这些核糖体充当5'至3'核糖核酸酶降解的屏障。此外，虽然先前发现红霉素仅在物理上稳定ermA转录本，但ermC-cat-86杂合转录本在物理和功能上均被红霉素稳定。
