Preferential cleavage of degradative intermediates of rpsT mRNA by the Escherichia coli RNA degradosome

RNase E, the principal RNase capable of initiating mRNA decay, preferential ly attacks 5'-monophosphorylated over 5'-triphosphorylated substrates. Site -specific cleavage in vitro of the rpsT mRNA by RNase H directed by chimeri c 2'-O-methyl oligonucleotides was employed to create truncated RNAs which are identical to authentic degradative intermediates. The rates of cleavage of two such intermediates by RNase E in the RNA degradosome are significan tly faster (2.5- to 8-fold) than that of intact RNA. This verifies the pref erence of RNase E for degradative intermediates and can explain the frequen t "all-or-none" behavior of mRNAs during the decay process.