MESSENGER-RNA PROCESSING INDEPENDENT OF RNASE-III AND RNASE-E IN THE EXPRESSION OF THE F1845 FIMBRIAL ADHESIN OF ESCHERICHIA-COLI

F1845, the fimbrial adhesin of a diarrhea-associated Escherichia coli, confers upon the bacteria the ability to adhere to cultured epithelial cells in a diffuse pattern. The fimbrial subunit gene, daaE, is encoded on a polycistronic mRNA which is processed endoribonucleolytically to produce a stable message encoding only daaE. The processing event occurs in bacterial strains with mutations in RNase III or RNase E, the only endoribonucleases which have been implicated in the processing of E. coli mRNA. Sequences encoding a stem-loop structure downstream of daaE play an essential role in determining the stability of the daaE mRNA. Rapid degradation of the sequences upstream of the cleavage site occurs upon processing, suggesting that processing of the F1845 polycistronic mRNA results in differential expression of genes involved in the biogenesis of fimbriae.