Processing of rRNA by RNAase P: spacer tRNAs are linked to 16S rRNA in an RNAase P RNAase III mutant strain of E. coli.

To determine which enzymes are responsible for the processing cleavages of ribosomal RNA transcripts in Escherichia coli, we constructed a mutant strain lacking RNAase III and containing a thermolabile RNAase P. At the nonpermissive temperature, this strain accumulates a novel "19S" RNA species which contains 17S precursor rRNA sequences covalently linked to tRNA sequences transcribed from the ribosomal RNA spacer region between the 16S and the 23S rRNA cistrons. In vitro treatment of 19S RNA with cell extracts releases tRNA2Glu and other tRNA species. These "spacer" tRNA sequences are apparently not contained with the 18S RNA species found in an RNAase III- RNAase P+ cell. RNAase P-deficient extracts are incapable of cleaving space tRNA from 19S RNA, indicating that RNAase P is required for the release of spacer tRNAs from rRNA transcripts of E. coli cells.