A unique mechanism regulating gene expression: translational inhibition by a complementary RNA transcript (micRNA).

The expression of the genes for the major outer membrane proteins OmpF and OmpC are osmoregulated. The ompC locus was found to be transcribed bidirectionally under conditions of high osmolarity and a 174-base transcript encoded upstream of ompC was found to inhibit the OmpF production and to substantially reduce the amount of the ompF mRNA. This RNA [mRNA-interfering complementary RNA (micRNA)] has a long sequence that is complementary to the 5' end region of the ompF mRNA. We propose that the micRNA inhibits the translation of the ompF mRNA by hybridizing with it. This RNA interaction may cause premature termination of the transcription of the ompF gene or destabilization of the ompF mRNA or both.