The mRNA derived MalH sRNA contributes to alternative carbon source utilization by tuning maltoporin expression in E. coli

摘要

Previous high-throughput studies in Gram-negative bacteria identified a large number of 3MODIFIER LETTER PRIMEUTR 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 3MODIFIER LETTER PRIME end ofmalG, which is part of the maltose uptake operon transcriptmalEFG. 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 reduceslamBaccumulation 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.