3'-EXORIBONUCLEOLYTIC TRIMMING IS A COMMON FEATURE OF THE MATURATION OF SMALL, STABLE RNAS IN ESCHERICHIA-COLI

In addition to tRNA and 5S RNA, Escherichia coil contains several othe r small, stable RNA species; these are M1, 10Sa, 6S, and 4.5S RNA. Alt hough these RNAs are initially synthesized as precursor molecules, rel atively little is known about their maturation. The data presented her e show that 3' exoribonucleolytic trimming is required for the final m aturation of each of these molecules. As found previously with tRNA, b ut not 5S RNA, any one of a number of exoribonucleases can carry out t he trimming reaction in vivo, although RNases T and PH are most effect ive. In their absence, large amounts of immature molecules accumulate for most of the RNAs, and these can be converted to the mature forms i n vitro by the purified RNases. A model is proposed that identifies a structural feature present in all the small, stable RNAs off. coil, an d describes how this structure together with the RNases influences the common mechanism for 3' maturation.