DNA unwinding by Escherichia coli DNA helicase I (TraI) provides evidence for a processive monomeric molecular motor.
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.
Sikora
Bartek
B
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
Eoff
Robert L
RL
Matson
Steven W
SW
Raney
Kevin D
KD
D000255:Adenosine Triphosphate / Q000737:chemistry; D020029:Base Pairing; D002384:Catalysis; D004247:DNA / Q000737:chemistry*; D004265:DNA Helicases / Q000502:physiology*; D004277:DNA, Single-Stranded / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000502:physiology*; D043211:Exodeoxyribonuclease V / Q000737:chemistry; D007700:Kinetics; D008957:Models, Genetic; D015233:Models, Statistical; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D013997:Time Factors
D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli; C027093:TraI protein, E coli; D004265:DNA Helicases