Extraordinary long-stem confers resistance of intrinsic terminators to processive antitermination

Abstract Many prokaryotic operons encode a processive antitermination (P-AT) system. Transcription complexes associated with an antitermination factor can bypass multiple transcription termination signals regardless of their sequences. However, to avoid compromising transcriptional regulation of downstream regions, the terminator at the end of the operon needs to be resistant to antitermination. So far, no studies on the mechanism of resistance to antitermination have been reported. The recently discovered conAn P-AT system is composed of two components that are encoded at the start of many conjugation operons on plasmids of Gram-positive bacteria. Here we report the identification of a conAn-resistant terminator, named TerR, in the conjugation operon of the Bacillus subtilis plasmid pLS20, re-defining the end of the conjugation operon. We investigated the various characteristics of TerR and show that its extraordinary long stem is the determining feature for resistance to antitermination. This is the first P-AT resistance mechanism to be reported. Graphical Abstract Graphical Abstract The long conjugation operon of plasmid pLS20 starts with a two-component antitermination system that antiterminates multiple intrinsic terminators located in the operon. Here, we identified an antitermination-resistant terminator located at the end of the conjugation operon that prevents undesired transcription of downstream regions.