A model for the mechanism of polymerase translocation.
A general mechanism for polymerase translocation is elaborated. The central feature of this mechanism is that a rapid translocational equilibrium is established after each cycle of nucleoside monophosphate incorporation such that the polymerase distributes itself by diffusional sliding between all accessible positions on the template with relative occupancy determined by relative free energy. While alternative models for translocation have not been fully developed, much of the language currently used to describe this step suggests an active mechanism coupled to conformational transitions in the polymerase. For example, a recent study of force generation by Escherichia coli RNA polymerase during transcription suggests that it is a mechanoenzyme analogous to kinesin of myosin motor proteins. While the proposed mechanism does not rule out conformational transitions during polymerase translocation, it suggests that they may be unnecessary and that translocation can be explained in terms of the affinity of the active site for nucleoside triphosphate and the relative free energies of the polymerase bound at different positions on the template. This mechanism makes specific predictions which are borne out experimentally with polymerases as distinct as E. coli DNAP I, phage T7 RNAP, and E. coli RNAP.
Guajardo
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R
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760, USA.
Sousa
R
R
D017123:Bacteriophage T7 / Q000201:enzymology / Q000235:genetics; D001665:Binding Sites; D001693:Biological Transport, Active; D004256:DNA Polymerase I / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D003854:Deoxyribonucleotides / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D007700:Kinetics; D008954:Models, Biological; D009154:Mutation; D012265:Ribonucleotides / Q000378:metabolism; D013816:Thermodynamics
D017931:DNA Primers; D003854:Deoxyribonucleotides; D012265:Ribonucleotides; D012321:DNA-Directed RNA Polymerases; D004256:DNA Polymerase I; D004259:DNA-Directed DNA Polymerase