ABSTRACT

Previous high-throughput studies in Gram-negative bacteria identified a large number of 3ʹUTR fragments that potentially function as sRNAs. Here we extensively characterize the MalH sRNA. We show that MalH is a stable degradation intermediate derived from the 3ʹ end of malG, which is part of the maltose uptake operon transcript malEFG. Unlike the majority of bacterial sRNAs, MalH is transiently expressed during the transition from the exponential to the stationary growth phase, suggesting that it contributes to adaptation to changes in nutrient availability. Over-expression of MalH reduces expression of general outer membrane porins and MicA, a repressor of the high-affinity maltose/maltodextrin transporter LamB. Disrupting MalH production and function significantly reduces lamB accumulation when maltose is the only available carbon source, presumably due to the accumulation of the MicA repressor. We propose that MalH is part of a regulatory network that, during the transition phase, directly or indirectly promotes accumulation of high-affinity maltose transporters in the outer membrane by dampening competing pathways.

摘要

先前对革兰氏阴性细菌的高通量研究发现了大量可能作为 sRNA 发挥作用的 3'UTR 片段。在这里，我们广泛地描述了 MalH sRNA。我们表明，MalH 是一种稳定的降解中间体，来源于malG的 3ʹ 端，它是麦芽糖摄取操纵子转录物malEFG的一部分。与大多数细菌 sRNA 不同，MalH 在从指数生长期到平稳生长期的过渡过程中短暂表达，这表明它有助于适应营养供应的变化。MalH 的过度表达降低了一般外膜孔蛋白和 MicA 的表达，MicA 是高亲和力麦芽糖/麦芽糖糊精转运蛋白 LamB 的阻遏物。破坏 MalH 的产生和功能会显着降低当麦芽糖是唯一可用的碳源时，lamB积累，可能是由于 MicA 阻遏物的积累。我们认为 MalH 是调节网络的一部分，在过渡阶段，通过抑制竞争途径直接或间接地促进高亲和力麦芽糖转运蛋白在外膜中的积累。