title: Visualization of ribosomal ribonucleic acid synthesis in a ribonuclease III-Deficient strain of Escherichia coli.
abstract: Transmission electron microscopy was used to examine active ribosomal ribonucleic acid (rRNA) genes in two strains of Escherichia coli: N2077, deficient in the enzyme responsible for proper cleavage of the 16S sequence from the elongating nascent rRNA transcript; and N2076, functional in ribonuclease (RNase) III activity, yet otherwise isogenic to N2077. In the strain with wild-type RNase III, double gradients corresponding to a pattern of 16S-cleavage-23S transcription were observed. However, the RNase III-deficient strain exhibited a single ribosomal gradient of approximately the same length as the combined 16S-23S gradients of the wild-type strain. When the rRNA genes were somewhat loosely packed with RNA polymerases, a few of the nascent chains in the ribosomal matrixes of the RNase III-deficient strain were cleaved, but most appeared to be unprocessed. The completed, uncleaved transcripts originating from these gradients are believed to be 30S rRNA molecules recently characterized by biochemical probes.
mesh_terms: D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D005796:Genes; D008854:Microscopy, Electron; D009154:Mutation; D012329:RNA, Bacterial / Q000096:biosynthesis*; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012260:Ribonucleases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D012321:DNA-Directed RNA Polymerases; D012260:Ribonucleases