TRANSLATION THROUGH AN UNCDC MESSENGER-RNA SECONDARY STRUCTURE GOVERNS THE LEVEL OF UNCC EXPRESSION IN ESCHERICHIA-COLI

Escherichia coli expresses the beta and epsilon subunits of F1F0-ATP s ynthase at relative levels consistent with the 3:1 (beta/epsilon) stoi chiometry in the holoenzyme. The mechanism of translational control of expression of the uncC gene (epsilon subunit) relative to the immedia tely 5' uncD gene (beta subunit) was examined. Previous expression stu dies and a computer analysis suggested the presence of an RNA secondar y structure including the 3' end of uncD, the uncDC intergenic region, and the uncC Shine-Dalgarno sequence (S. D. Dunn and H. G. Dallmann, J. Bacteriol. 172:2782-2784, 1990). Analysis of in vitro-transcribed R NA by cleavage,vith RNases T-1, V-1, and CL3 and by chemical modificat ion with dimethyl sulfate and diethyl pyrocarbonate confirmed a predic ted structure. Introduction of premature uncD stop codons inserted 5' of the secondary structure strongly reduced epsilon expression, wherea s stop codons inserted at positions within the secondary structure sho wed smaller effects, indicating that translational control of epsilon synthesis involves partial coupling to beta synthesis. Possible mechan isms by which the RNA secondary structure and the unfolding of this st ructure by translation of uncD may govern the level of uncC expression are discussed.