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Nucleic Acids Research, 1995, Vol. 23, No. 21 4443-4450
© 1995

Articles

Purification and characterisation of a DNA helicase,dhel I, from sophila melanogasterembryos

Pia Thömmes+, F. Marton and Sue Cotterill*

Marie Curie Research Institute The Chart, Oxted, Surrey RH8 0TL, UK

*To whom correspondence should be addressed

Received July 3, 1995. Accepted October 2, 1995.

We have purified a DNA helicase (dhel I) from early Drosophila embryos, dhel I co-purifies with the singlestranded DNA binding protein dRP-A over two purification steps, however, the proteins can be separated by their different native molecular weight, with dhel I activity co-sedimenting with a polypeptide of -200 kDa and a sedimentation coefficient of 8.6 S. The enzyme needs ATP hydrolysis and divalent cations for displacement activity. It is very salt sensitive, having a Mg2+ optimum of 0.5 mM and being inhibited by NaCI concentration >10 mM. Dhel I moves 5prime;->3' on the DNA strand to which it is bound. Unwinding activity decreases with increasing length of the doublestranded region suggesting a distributive mode of action. However, addition of dRP-A to the displacement reaction stimulates the activity on substrates with >300 nucleotides double-stranded region suggesting a specific interaction between these two proteins.

+Present address: Imperial Cancer Research Fund, Clare Hall Laboratories, Blanche Lane, South Mimms, Potters Bar, Herts EN6 3LD, UK


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