RT Journal Article SR Electronic(1) A1 Ji, Yuan-en A1 Colston, M Joseph A1 Cox, Robert A.YR 1994 T1 The ribosomal RNA (rrn) operons of fast-growing mycobacteria: primary and secondary structures and their relation to rrnoperons of pathogenic slow-growers JF Microbiology, VO 140 IS 10 SP 2829 OP 2840 DO https://doi.org/10.1099/00221287-140-10-2829 PB Microbiology Society, SN 1465-2080, AB The two ribosomal RNA (rrn) operons (rrnAand rrnB) of Mycobacterium smegmatiswere investigated. The leader regions, part of the 16S rRNA genes, the spacer-1 regions, part of the 23S rRNA genes, and the spacer-2 regions were amplified by PCR or by inverse PCR and the products were cloned and sequenced. No differences in the sequences of the two operons were detected downstream from the Box A antitermination element of the leader region. Upstream from Box A a slow-grower-like Box B antitermination element was found in rrnAbut not in rrnB.Primer extension experiments revealed that the start of transcription lies at least 370 nucleotides upstream from the 5′-end of the 16S rRNA gene and an RNase processing site near to the Box A element. Secondary structures were deduced for pre-16S rRNA and pre-23S rRNA which are distinct from, but closely related to, the corresponding structures of slow-growing mycobacteria. On the basis of these results it is proposed that the emergence of the slow-growers from the main mycobacterial line was coincident with the deletion of a segment of DNA spanning an rrnB-like operon, leaving an rrnA-like operon as the sole source of rRNA. An explanation is also proposed for the need for two Box A motifs in the transcription of an rrnoperon based on competition between the polymerase and the nascent 30S subunit for either protein S10 and/or Box A sequences., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-140-10-2829