PURIFICATION AND CHARACTERIZATION OF THE RECD PROTEIN-HOMOLOGUE FROM DEINOCOCCUS RADIODURANS

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dc.contributor.advisorJulin, Douglas Aen_US
dc.contributor.authorWang, Jianleien_US
dc.contributor.departmentBiochemistryen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2005-02-02T06:52:23Z
dc.date.available2005-02-02T06:52:23Z
dc.date.issued2004-12-06en_US
dc.description.abstractIn many gram-negative bacteria, RecBCD enzyme is found to be responsible for double strand DNA break repair through homologous recombination. The AddAB enzyme, a RecBCD analog, is found in some gram-positive bacteria and functions in a similar way as RecBCD. A few bacteria appear to lack both RecBCD and AddAB enzymes entirely. One such organism is the bacterium Deinococcus radiodurans. This remarkable organism is able to survive in the presence of very high levels of radiation or DNA-damaging chemicals, levels that would overwhelm the DNA repair capacity of most other organisms. Interestingly, the D. radiodurans genome does have an open reading frame that would encode a protein that is homologous to the E. coli RecD protein. The amino acid sequence of this D. radiodurans RecD-like protein suggests that it is a helicase and therefore could function in some aspect of DNA repair, as does its E. coli homologue. However, the RecD protein of D. radiodurans must serve a different and novel function compared to the E. coli RecD protein. The D. radiodurans RecD protein can be expressed at high levels in E. coli and is readily purified by chromatography on a nickel column followed by single-stranded DNA-cellulose. The purified protein exhibits DNA-dependent ATPase and DNA helicase activities. The helicase activity requires at least a 10 nucleotide single strand overhang at the 5'-end of the double strand DNA substrate to start unwinding. The helicase assay shows that D. radiodurans RecD-like protein unwinds dsDNA substrates catalytically, but with low processivity, even with the help of single strand binding proteins (SSB) from either E. coli or D. radiodurans. These results show that D. radiodurans RecD-like protein is a DNA helicase that moves with 5'-3' polarity on single-stranded DNA. The E. coli RecD protein was shown recently to unwind dsDNA with the same 5'-3' polarity. The low processivity of the D. radiodurans RecD-like protein suggests that it may function in a complex with other proteins. The identity of these proteins is not known. We have also generated insertion mutations that are likely to disrupt all of the <i>recD</i> gene copies in the <i>D. radiodurans</i> genome after multiple generations growing in media with antibiotics. The <i>in vivo</i> effects of the insertion mutation, such as the growth curve and the sensitivity to UV radiation and DNA damaging chemicals, were studied.en_US
dc.format.extent2306882 bytes
dc.format.mimetypeapplication/pdf
dc.identifier.urihttp://hdl.handle.net/1903/2139
dc.language.isoen_US
dc.subject.pqcontrolledChemistry, Biochemistryen_US
dc.subject.pquncontrolledD. radioduransen_US
dc.subject.pquncontrolledRecBCDen_US
dc.subject.pquncontrolledRecDen_US
dc.subject.pquncontrolledHelicaseen_US
dc.subject.pquncontrolledDNA repairen_US
dc.subject.pquncontrolledDNA replicationen_US
dc.titlePURIFICATION AND CHARACTERIZATION OF THE RECD PROTEIN-HOMOLOGUE FROM DEINOCOCCUS RADIODURANSen_US
dc.typeDissertationen_US

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