title: A conditional lethal mutant of Escherichia coli which affects the processing of ribosomal RNA.
abstract: A temperature-sensitive mutant strain was isolated from an RNase III-(rnc) strain of Escherichia coli. At the permissive temperature it behaves like the parental strain, but at the nonpermissive temperature it fails to produce normal levels of 23 S and 5 S rRNA, while instead the 25 S rRNA species becomes very prominent. (The 25 S molecule appears in rnc cells and contains 23 S rRNA sequences). When an rnc+ mutation was introduced to such a strain, or when the rnc mutation was replaced by an rnc+ allele, the strain remained temperature-sensitive. At the permissive temperature such strains synthesized rRNA like any other E. coli strain, but at the nonpermissive temperature they remained unable to synthesize normal levels of 5 S rRNA, and instead a larger molecule was accumulated. The simplest interpretation of theses findings is that the mutant strain contains a temperature-sensitive processing endoribonuclease, RNase E, which normally introduces a cut in the growing rRNA chain somewhere between the 23 S and the 5 S rRNA cistrons. These findings help also to explain the nature and origin of the various rRNA species observed in RNase III- cells and add to our understanding of processing of ribosomal RNA in normal cells of Escherichia coli.
mesh_terms: D000483:Alleles; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005804:Genes, Lethal; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D012260:Ribonucleases; D014158:Transcription, Genetic
chemical_list: D012335:RNA, Ribosomal; D012260:Ribonucleases