Intrinsic transcription termination of bacteriophage RNA polymerases : characterization of two types of termination signal

Abstract

The bacteriophage T7 and SP6 RNA polymerases terminate transcription on two types of termination signal without help of any factors. One of the two types of intrinsic termination mechanism involves an RNA hairpin structure and the other does not. Some novel properties of the two mechanisms are characterized here in detail. Termination efficiency of the bacteriophage T7 RNA polymerase at the intrinsic, hairpin-dependent terminator of bacteriophage T7 can be reduced by the G-rich abortive transcripts produced from the T7 promoter [Kwon, Y.-S. (1993) Master Thesis, KAIST, Taejon, Republic of Korea]. To identify the mechanism of termination efficiency reduction by the G-rich abortive transcripts, the specificity of the termination efficiency reduction was examined. Termination efficiency was reduced only for the T7 terminator. All the other terminators examined show constant termination efficiencies regardless of the presence of such abortive transcripts. When the transcribing RNA polymerases were other phage-encoded RNA polymerases, the abortive transcripts reduced termination efficiency at the T7 terminator. The efficiency reduction by abortive transcripts was abolished when mutations were introduced in a region encoding the base part of hairpin structure in nascent transcripts. However, mutations in other parts do not invoke the resistance to the influence of abortive transcripts on termination efficiency. Thus, the abortive transcripts produced from the T7 promoter appear to interfere with termination through base-specific interaction. The region of nascent transcript that interacts with the abortive transcripts constitutes a part of the essential hairpin-forming secondary structure. The transcript off the T7 terminator can form a stable hairpin structure, followed by a run of rU. In order to identify the elements that are required for termination, the termination efficiencies of T7 RNA polymerase, SP6 RNA polymerase and nicked SP6 RNA polymerase at a variety...