MICF ANTISENSE RNA HAS A MAJOR ROLE IN OSMOREGULATION OF OMPF IN ESCHERICHIA-COLI

micF RNA, produced from a multicopy plasmid, was originally shown to b e a major factor in negative osmoregulation of the OmpF outer membrane protein in Escherichia coli. However, subsequent experiments with a m icF deletion strain suggested that chromosomal micF RNA was not a key component in this process. We report here that micF RNA is essential f or the reduction in OmpF levels in cells grown in media of low-to-inte rmediate levels of osmolarity. Under these conditions, the amount of O mpF was reduced up to 60% in the parent strain while OmpF levels were not altered in the micF deletion mutant: In medium of higher osmolarit y, OmpF synthesis was strongly inhibited in both strains. RNA measurem ents showed that micF RNA levels rose rapidly in cells grown in low-to -intermediate levels of osmolarity concomitant with the reduction in O mpF protein, while ompF mRNA decreased strongly only during high-osmol arity conditions. Taken together, these results strongly suggest that the negative osmoregulation of OmpF at low-to-intermediate osmolarity levels requires micF RNA and that this is masked at higher osmolarity by the known strong inhibition of OmpF transcription by OmpR. Results consistent with this model were also obtained by using procaine, a com pound reported to inhibit ompF expression by a mechanism very similar to that involved in osmoregulation.