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Functional similarities between phage Orf and Escherichia coli RecFOR in initiation of genetic exchange

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Publication date2006
Number of pages0
Original languageEnglish
EventSociety for General Microbiology 159th Meeting - York, United Kingdom
Duration: 11/09/200614/09/2006

Conference

ConferenceSociety for General Microbiology 159th Meeting
CountryUnited Kingdom
CityYork
Period11/09/0614/09/06

Abstract

Genetic recombination in bacteriophage lambda relies on DNA end processing by Exo to expose 3’ tailed strands for annealing and exchange by Beta protein. Phage lambda encodes an additional recombinase, Orf, which participates in the early stages of recombination by supplying a function equivalent to the E. coli RecFOR complex. These host enzymes assist loading of the RecA strand exchange protein onto ssDNA coated with SSB. We have purified distantly-related Orf proteins from lambda and E. coli DLP12 prophage. Both Orf proteins bind DNA, favouring single-stranded over duplex and show no obvious preference for gapped, 3′or 5′tailed substrates. The crystal structure of lambda Orf reveals a homodimer arranged as a toroid with a shallow U-shaped cleft, lined with basic residues, running perpendicular to the central cavity. Gapped duplex DNA binding experiments suggest that DNA is accommodated on the surface cleft. Both Orf homologs appear to interact with E. coli SSB and we present evidence that they associate together on DNA. The functional similarities between Orf and RecFOR are discussed in relation to the early steps of recombinational exchange and the interplay between phage and bacterial recombinases.