IS-10 MESSENGER-RNA STABILITY AND STEADY-STATE LEVELS IN ESCHERICHIA-COLI - INDIRECT EFFECTS OF TRANSLATION AND ROLE OF RNE FUNCTION

Translation of the IS10 transposase gene is known to be very infrequen t. We have identified mutations whose genetic properties suggest that they act directly to increase or decrease the intrinsic level of trans lation initiation. Also, we have analysed in detail the effects of the se mutations on IS10 mRNA using one particular IS10 derivative. In thi s case, increases or decreases in translation are accompanied by incre ases or decreases in both the steady state level and the half-life of transposase mRNA; effects on steady state levels are much more dramati c than effects on message half-life. At wild-type levels of translatio n initiation, the rate-limiting step in physical decay of full length IS10 message for a particular IS10 derivative is shown to be rne-depen dent endonucleolytic cleavage; 3' exonucleases appear to play a second ary role, degrading primary cleavage products. Analysis of interplay b etween translation mutations and me function, together with the above observations, suggests that translation stabilizes messages in a gener al way against rne-dependent endonucleolytic cleavage , and that signi ficant protection may be conferred by one or a few ribosomes. However, dramatic effects of translation on steady state message levels are st ill observed in an me mutant and involve the 3' end of the transcript; we propose that these additional effects reflect translation-mediated stimulation of transcript release.