THE ACINETOBACTER-CALCOACETICUS NCIB8250 MOP OPERON MESSENGER-RNA IS DIFFERENTIALLY DEGRADED, RESULTING IN A HIGHER-LEVEL OF THE 3'-CATA-ENCODING SEGMENT THAN OF THE 5'-PHENOLHYDROXYLASE-ENCODING PORTION

The 7.5-kb polycistronic mop mRNA is differentially degraded in Acinet obacter calcoaceticus. The 4.9-kb 5' portion of the transcript contain s the genes mopKLMNOP, encoding the multi-component phenol hydroxylase , and its 5' end decays three times faster than the 2.3-kb 3' portion encoding catechol 1,2-dioxygenase (catA). Larger amounts of the catA m RNA than the mopKLMNOP mRNA are present in the cells as a result of th is processing. The site for endonucleolytic cleavage is located in the intercistronic region between mopP and catA, and contains a potential stem-loop structure and a putative RNase E cleavage site. Decay of th e mop mRNA in Escherichia coli depends on RNase E. Thus, we propose th at an RNase E-like activity is also present in A. calcoaceticus. Expre ssion of MopN, one polypeptide of the multi-component phenol hydroxyla se, interferes with growth of A. calcoaceticus. Thus, harmful expressi on of MopN may be reduced by rapid decay of its mRNA, indicating that mRNA processing contributes to differential gene expression in the lar ge mop operon of A. calcoaceticus NCIB8250.