Transcriptional Organization of the Ribosomal RNA Cistrons in Escherichia Coli

Abstract

The data presented support the hypothesis that 16S, 23S, and 5S ribosomal RNAs of Escherichia coli are transcribed in vivo from transcriptional units consisting of single cistrons for these species arranged in the order 16S-23S-5S, with transcription beginning at the 16S end.In eukaryotic cells, linked 18S, 28S, and 7S ribosomal RNA cistrons are transcribed as a unit into a single polynucleotide "precursor" (45S rRNA), which is ultimately cleaved to produce one molecule of each of the three rRNA species (1, 2). The three linked cistrons together comprise a single "transcriptional unit", which we define here as a segment of DNA bounded by a single site for RNA polymerase attachment (promoter) and a single site for polymerase release (terminator). Many such rRNA transcriptional units are confined to a restricted region of the eukaryotic chromosome; adjacent units may be separated by a segment of (nonribosomal) "spacer" DNA (1).The genetic organization of the cistrons for bacterial rRNA species (16S, 23S, and 5S rRNA) is similar to that of eukaryotes in that: (a) the number of gene copies (per genome) for each RNA species is the same (3, 4), (b) these cistrons are confined to one (5) or possibly two (6, 7) small regions of the genome, (c) 16S, 23S, and 5S rRNA cistrons are tightly linked (8, 9), and (d) adjacent 16S, 23S, and 5S gene clusters are separated from each other by segments of spacer DNA (10).Data presented here support the hypothesis that the linked 16S, 23S, and 5S rRNA cistrons in Escherichia coli comprise single transcriptional units arranged in the order 16S-23S-5S, with transcription initiating at the 16S end. The fact that no "precursor" comparable to eukaryotic 45S rRNA has yet been found in bacteria may imply that cleavage into 16S and 23S (and possibly 5S) moieties occurs before transcription of the unit is complete. MATERIALS AND METHODSFor the preparation of intact 3H-labeled RNA from rifampicininhibited cells, a culture of the rifampicin-sensitive, E. coli B strain AS19 (11) Corp.), was chased by the addition of excess unlabeled orthophosphate, and after 30 min of further growth at 200C, was chilled to 00C in ice. Rifampicin (Pittman-Moore) was added to 200 Ag/ml at 2 min and [5-3H]uridine (New England Nuclear Corp.) was added to 0.04 mCi/ml (10 ;&g/ml) at 4 min after chilling. At 6 min the culture was warmed to 20'C and incubation was continued for an additional 40 min. Cultures were harvested by centrifugation and RNA was extracted and resolved on 2.8% polyacrylamide gels (13,14).For the preparation of RNA for oligonucleotide mapping,

Ribosomal Ribonucleic Acid Synthesis and Maturation in the Blue-Green Alga Anacystis nidulans

“…rRNA precursors substantially larger than p16 and p23 have not been identified in bacteria. In particular, no single large RNA chain containing both 16S and 23S rRNA sequences has been found (5,10). This situation is in strong contrast to that in eukaryotes, in which the major rRNA species are both derived from a single, easily detected, high-molecular-weight (41 to 45S) precursor (6).…”

Molecular Genetic Basis of Ribotyping

“…Because the 16S rRNA gene is the most conserved of the three rRNA genes, 16S rRNA gene sequencing has been established as the "gold standard" for identification and taxonomic classification of bacterial species (41,61,90). Knowledge of intraspecies conservation of the 16S rRNA gene sequence (21) and basic 16S-23S-5S ribosomal operon structure (17) led Grimont and Grimont (25) to the first insights into its usefulness in developing ribotyping for bacterial classification.…”

“…rRNA genes are typically transcribed from the ribosomal operon as 30S rRNA precursor molecules which are then cleaved by RNase III into 16S, 23S, and 5S rRNA molecules (17,59,77). Winkler was the first to observe fragmentation of 23S rRNA molecules of Salmonella enterica serovar Typhimurium into several smaller molecules during maturation (88).…”

Unique ribosome structure of Leptospira interrogans is composed of four rRNA components

“…The rRNA of the eucaryotic cells is also processed in a similar way during maturation, but it has an extra cleavage site near the 5' end of the large-subunit rRNA to generate 18, 28, 5, and 5.8S rRNAs. The 18S rRNA is homologous to the procaryotic 16S rRNA (small-subunit rRNA), and the 28 and 5.8S rRNAs together are homologous to the 23S rRNA (large-subunit rRNA) of the procaryotic cells (3,4,9).Though most eucaryotic large-subunit rRNAs contain only one extra cleavage site compared with procaryotic large-subunit rRNAs, some eucaryotic organisms have been reported to contain more cleavage sites. These organisms include protostomes, protozoa, and some coelenterates (2,8,20).…”

“…The rRNA of the eucaryotic cells is also processed in a similar way during maturation, but it has an extra cleavage site near the 5' end of the large-subunit rRNA to generate 18, 28, 5, and 5.8S rRNAs. The 18S rRNA is homologous to the procaryotic 16S rRNA (small-subunit rRNA), and the 28 and 5.8S rRNAs together are homologous to the 23S rRNA (large-subunit rRNA) of the procaryotic cells (3,4,9).…”