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A Recombinase from Drosophila melanogaster Embryos

Andrew Eisen and R. Daniel Camerini-Otero
Proceedings of the National Academy of Sciences of the United States of America
Vol. 85, No. 20 (Oct. 15, 1988), pp. 7481-7485
Stable URL: http://www.jstor.org/stable/32967
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Recombinase from Drosophila melanogaster Embryos
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Abstract

We have partially purified a DNA strand-exchange activity (recombinase) from nuclear extracts of Drosophila melanogaster embryos. The protein fraction forms a joint molecule between a circular single-strand DNA and a homologous linear duplex DNA that is resolved from the substrates by agarose gel electrophoresis. A strand-exchange activity can be obtained from nuclear extracts from embryos as old as 24 hr. The activity is similar to that partially purified from human cells [Hsieh, P., Meyn, S. M. & Camerini-Otero, R. D. (1986) Cell 44, 885-894]. It is homology-dependent, requires Mg2+, appears to be directional in that it prefers to displace the 3 end of the noncomplementary strand, and does not require exogenous ATP. Forty nanograms of protein in the partially purified DNA strand-exchange fraction from D. melanogaster embryos can completely convert 50 ng of substrate single-strand DNA into joint molecules in 10 min. In the electron microscope, joint molecules are seen to consist of a circular single-strand DNA molecule attached to only one end of a linear duplex DNA molecule; a displaced strand is also seen. The region of heteroduplex formation can be as long as 600 base pairs. The demonstration of a strand-exchange activity from wild-type D. melanogaster embryos invites analysis of recombination-defective mutants to explore the role of DNA strand exchange in homologous recombination.

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