The function of micF RNA. micF RNA is a major factor in the thermal regulation of OmpF protein in Escherichia coli

The role of chromosomally derived micF RNA as a repressor of outer membrane protein OmpF of Escherichia coli was examined for various growth conditions. Levels of micF RNA as determined by Northern analyses are found to increase in response to cell growth at high temperature, in high osmolarity or in the presence of ethanol. After a switch to higher growth temperature, the levels of ompF mRNA and of newly synthesized OmpF decrease with time in E. coli strain, MC4100 but these decreases are not observed in isogenic micF deletion strain, SM3001. In addition, while levels of ompF mRNA are substantially reduced in both strains in response to high osmolarity or ethanol at 24 degrees C, the reduced levels in the parental strain are still 4-5-fold lower compared with the micF deletion strain. These findings indicate that chromosomally derived micF RNA plays a major role in the thermal regulation of OmpF and represses OmpF synthesis in response to several environmental signals by decreasing the levels of ompF mRNA. Analyses of the effect of a multicopy micF plasmid on the levels of OmpF and ompF mRNA after an increase in temperature indicated that multicopies of micF RNA markedly inhibited OmpF synthesis but did not accentuate ompF mRNA decrease. These data suggest that multicopy micF inhibits OmpF synthesis primarily through translational inactivation of ompF mRNA and that a limiting factor in addition to micF RNA is necessary to destabilize ompF mRNA.     

micF RNA in ompB mutants of Escherichia coli: different pathways regulate micF RNA levels in response to osmolarity and temperature change.

The repressor RNA, micF RNA, is regulated by temperature, osmolarity, and other stress conditions during growth of Escherichia coli. Northern (RNA) blot analyses showed that levels of micF RNA differ widely in various ompB mutant strains when cells are grown at 24 degrees C in LB broth. For example, relative to the parental strain MC4100, the ompR101 mutant strain (which contains no functional OmpR) had about a 10-fold reduction in micF RNA, whereas the envZ11 strain showed about a 5-fold increase. At 37 degrees C, however, micF RNA levels in the ompR101 and envZ11 strains and other ompB mutants differed by less than two-fold compared with the level in strain MC4100, thus indicating that a factor(s) independent of the ompB locus regulates micF RNA expression with temperature increase and that there is an additional control mechanism(s) which maintains the levels of micF RNA in these mutants close to that of the wild type during growth at high temperatures. In a plasmid strain containing the micF gene but without the upstream OmpR-binding site, steady-state levels of micF RNA increased with temperature increase but did not change with osmolarity increase. This showed that osmolal regulation but not temperature regulation of micF depends on these upstream sequences and suggested that while osmolal regulation of the micF gene depends on OmpR, thermal regulation does not.     

Vascular-specific expression of the bean GRP 1.8 gene is negatively regulated.

In French bean, the glycine-rich cell wall protein GRP 1.8 is specifically synthesized in the vascular tissue. To identify cis-acting sequences required for cell type-specific synthesis of GRP 1.8, expression patterns of fusion gene constructs were analyzed in transgenic tobacco. In these constructs, the uidA (beta-glucuronidase) gene was placed under control of 5' upstream deletions as well as internal deletions of the GRP 1.8 promoter. Four different cis-acting regulatory regions, SE1 and SE2 (stem elements), a negative regulatory element, and a root-specific element, were found to control the tissue-specific expression. Deletion of the negative regulatory element resulted in expression of the uidA gene in cell types other than vascular cells. The SE1 region was essential for expression in several cell types in the absence of further upstream regulatory sequences. Full-length promoters having insertions between the negative regulatory element and SE1 strongly expressed the gene in nonvascular cell types in stems and leaves. Thus, vascular-specific expression of the GRP 1.8 promoter is controlled by a complex set of positive and negative interactions between cis-acting regulatory regions. The disturbance of these interactions results in expression in additional cell types.