The SbcCD complex mediates the inviability of long palindromes in <I>Escherichia coli.</I> The eukaryotic homologues, Rad50Mre11, are involved in DSB formation and the human homologues have been implicated in cancer progression. In this work a biochemical characterisation of the hairpin nuclease activity has been undertaken to help elucidate its cellular roles and those of its homologues. It was intended to map the sites of hairpin cleavage and to determine the chemical nature of the cleaved termini. The nuclease requirements for substrate structure were to be examined to test the model for palindrome maintenance. In this regard, it was to be determined whether substrate termini were required. In addition it was intended to discover whether SbcCD possesses a helicase activity. A DNA binding assay was sought to define alternative substrates and thence alternative potential roles of the protein, and to detail the protein substrate interaction. It has been shown that hairpin cleavage occurs immediately 5' of the loop and is followed by stem degradation. Cleavage and degradation have been uncoupled. The cleavage products have 5' phosphate and 3' hydroxyl termini. A dumbell substrate lacking termini was generated and found to be cleaved, supporting the model and suggesting that SbcCD is involved in DSB formation like its homologues. SbcCD has been shown not to posses a helicase activity on a hairpin substrate. DNA binding has been demonstrated by gel filtration and studied by gel retardation. It is proposed that SbcCD may bind its substrate transiently.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653466 |
| Date | January 1999 |
| Creators | Kirkham, Lucy A. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15183 |
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