Dissociation of halted T7 RNA polymerase elongation complexes proceeds via a forward-translocation mechanism
Biochemistry & Molecular Pharmacology
Graduate School of Biomedical Sciences; Department of Psychiatry, Brudnick Neuropsychiatric Research Institute
Medical Subject Headings
Base Sequence; Biological Transport; DNA, Viral; DNA-Directed RNA Polymerases; Enzyme Stability; Escherichia coli; Kinetics; Models, Genetic; Mutation; Promoter Regions (Genetics); Templates, Genetic; Transcription, Genetic; Viral Proteins
Life Sciences | Medicine and Health Sciences
A recent model for the mechanism of intrinsic transcription termination involves dissociation of the RNA from forward-translocated (hypertranslocated) states of the complex [Yarnell WS, Roberts JW (1999) Science, 284:611-615]. The current study demonstrates that halted elongation complexes of T7 RNA polymerase in the absence of termination signals can also dissociate via a forward-translocation mechanism. Shortening of the downstream DNA or the introduction of a stretch of mismatched DNA immediately downstream of the halt site reduces a barrier to forward translocation and correspondingly reduces the lifetime of halted complexes. Conversely, introduction of a cross-link downstream of the halt site increases the same barrier and leads to an increase in complex lifetime. Introduction of a mismatch within the bubble reduces a driving force for forward translocation and correspondingly increases the lifetime of the complex, but only for mismatches at the upstream edge of the bubble, as predicted by the model. Mismatching only the two most upstream of the eight bases in the bubble provides a maximal increase in complex stability, suggesting that dissociation occurs primarily from early forward-translocated states. Finally, addition in trans of an oligonucleotide complementary to the nascent RNA just beyond the hybrid complements the loss of driving force derived from placement of a mismatch within the bubble, confirming the expected additivity of effects. Thus, forward translocation is likely a general mechanism for dissociation of elongation complexes, both in the presence and absence of intrinsic termination signals.
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Citation: Proc Natl Acad Sci U S A. 2007 Jun 19;104(25):10352-7. Epub 2007 Jun 6. Link to article on publisher's site
Proceedings of the National Academy of Sciences of the United States of America
Zhou, Yi; Navaroli, Deanna M.; Enuameh, Metewo Selase; and Martin, Craig T., "Dissociation of halted T7 RNA polymerase elongation complexes proceeds via a forward-translocation mechanism" (2007). GSBS Student Publications. 433.