Title: DNA unwinding by Escherichia coli DNA helicase I (TraI) provides evidence for a processive monomeric molecular motor. | Journal: The Journal of biological chemistry. 2006 Nov;281(47):36110-6 | Authors: Sikora B, Eoff RL, Matson SW, Raney KD. | Abstract: The F plasmid TraI protein (DNA helicase I) plays an essential role in conjugative DNA transfer as both a transesterase and a helicase. Previous work has shown that the 192-kDa TraI protein is a highly processive helicase, catalytically separating >850 bp under steady-state conditions. In this report, we examine the kinetic mechanism describing DNA unwinding of TraI. The kinetic step size of TraI was measured under both single turnover and pre-steady-state conditions. The resulting kinetic step-size estimate was approximately 6-8 bp step(-1). TraI can separate double-stranded DNA at a rate of approximately 1100 bp s(-1), similar to the measured unwinding rate of the RecBCD helicase, and appears to dissociate very slowly from the 3' terminus following translocation and strand-separation events. Analyses of pre-steady-state burst amplitudes indicate that TraI can function as a monomer, similar to the bacteriophage T4 helicase, Dda. However, unlike Dda, TraI is a highly processive monomeric helicase, making it unique among the DNA helicases characterized thus far. | See full PubMed entry: http://www.ncbi.nlm.nih.gov/pubmed/16984922 |
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