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Nucleic Acids Research, 2002, Vol. 30, No. 13 2809-2816
© 2002 Oxford University Press

Modulation of enzymatic activities of Escherichia coli DnaB helicase by single-stranded DNA-binding proteins

Esther E. Biswas1,2, Pei-Hua Chen1 and Subhasis B. Biswas1,*

1 Department of Molecular Biology and School of Osteopathic Medicine and Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 2 Medical Center Drive, Stratford, NJ 08084, USA and 2 Program in Biotechnology, Department of Laboratory Sciences, Thomas Jefferson University, Philadelphia, PA 1907, USA

The modulation of enzymatic activities of Escherichia coli DnaB helicase by homologous and heterologous single-stranded DNA-binding proteins (SSBs) and its DNA substrates were analyzed. Although DnaB helicase can unwind a variety of DNA substrates possessing different fork-like structures, the rate of DNA unwinding was significantly diminished with substrates lacking a 3' fork. A 5 nt fork appeared to be adequate to attain the maximum rate of DNA unwinding. Efficient helicase action of DnaB requires the participation of SSBs. Studies involving heterologous SSBs demonstrated that they can stimulate the helicase activity of DnaB protein under certain conditions. However, this stimulation occurs in a manner distinctly different from that observed with cognate E.coli SSB. The E.coli SSB was found to stimulate the helicase activity over a wide range of SSB concentrations and was unique in its strong inhibition of single-stranded DNA-dependent ATPase activity when uncoupled from the DNA helicase activity. In the presence of a helicase substrate, the ATPase activity of DnaB helicase remained uninhibited. Thus, E.coli SSB appears to coordinate and couple the ATPase activity to the DNA helicase activity by suppressing unproductive ATP hydrolysis by DnaB helicase.

* To whom correspondence should be addressed. Tel: +1 856 566 6270; Fax: +1 781 207 8476; Email: biswassb{at}umdnj.edu


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