Hahn J, Grandi G, Gryczan T J, Dubnau D
Mol Gen Genet. 1982;186(2):204-16. doi: 10.1007/BF00331851.
ermC is a plasmid gene which specifies resistance to macrolide-lincosamide-streptogramin B antibiotics. The product of ermC was previously shown to be an inducible rRNA methylase, which is regulated translationally, and a mechanism for this regulation, termed the translational attenuation model, has been proposed. This model postulates that alternative inactive and active conformational states of the ermC mRNA are modulated by erythromycin-induced ribosome-stalling during translation of a leader peptide. In the present study the translational attenuation model was tested by constructing a series of deletants missing the ermC promoter and portions of the regulatory (leading) region. In these mutants, ermC transcription is dependent on fusion to an upstream promoter. Depending on the terminus of each deletion within the regulatory region, determined by DNA sequencing, ermC expression is observed to be either high level and inducible (like the wild-type), high level and noninducible, or low level and noninducible. The translational attenuation model predicts that as the deletions extend deeper into the leader region, successively masking and unmasking sequences required for translation of the methylase, an alternation of high and low level methylase expression will be observed. These predictions are confirmed. Based on this and other information, the model is refined and extended, and both direct translational activation and kinetic trapping of a metastable active intermediate during transcription are proposed to explain basal synthesis of methylase and to rationalize the effects of certain regulatory mutants.
ermC是一种质粒基因，它赋予对大环内酯-林可酰胺-链阳菌素B类抗生素的抗性。ermC的产物先前已被证明是一种可诱导的rRNA甲基化酶，其受翻译水平调控，并且已经提出了一种称为翻译衰减模型的调控机制。该模型假定，ermC mRNA的交替无活性和活性构象状态在引导肽翻译过程中受红霉素诱导的核糖体停滞调节。在本研究中，通过构建一系列缺失ermC启动子和部分调控（引导）区域的缺失体来测试翻译衰减模型。在这些突变体中，ermC转录依赖于与上游启动子的融合。根据DNA测序确定的调控区域内每个缺失的末端，观察到ermC表达要么是高水平且可诱导的（如野生型）、高水平且不可诱导的，要么是低水平且不可诱导的。翻译衰减模型预测，随着缺失向引导区域深入延伸，依次掩盖和暴露甲基化酶翻译所需的序列，将观察到甲基化酶表达的高低水平交替。这些预测得到了证实。基于此及其他信息，对该模型进行了完善和扩展，并提出了转录过程中直接翻译激活和亚稳态活性中间体的动力学捕获，以解释甲基化酶的基础合成并合理化某些调控突变体的作用。
