From studies of DNA repair and recombination, it is apparent that nucleases play a major role in both of these processes. In S. cerevisiae the RAD52 gene is essential for the repair of DNA double-strand breaks, mitotic recombination and for the successful completion of meiosis. A 72 kD nuclease (RhoNUC) has been identified and subsequently purified. In rad52 mutants, levels of RhoNuc are greatly decreased suggesting that this nuclease is under the control of RAD52. The gene encoding RhoNUC has been cloned and sequenced. OFAGE analysis places the gene encoding RhoNUC (RNC1) on chromosome XI. Examination of the deduced primary sequence from the DNA sequence reveals that RhoNUC is a chimeric protein. The N-terminal region of the protein shares a high degree of homology with the ras/rho superfamily of GTP binding proteins while the C-terminal appears to encode the nuclease portion of the protein. Hence, this protein has been named RhoNUC for rho-associated nuclease. By utilizing a RNC1::lacZ fusion construct in strains that either contain a wild type RAD52 gene or a complete deletion of RAD52, it appears that the control of RhoNUC by RAD52 is post-translational. Overexpression of RNC1 gene yields no observable phenotype. However, strains carrying deletions of both RNC1 and RAD52 have nearly wild-type levels of direct repeat recombination when measured either on plasmids or on the chromosome (strains carrying only a deletion of RAD52 exhibit recombination levels approximately 100-fold lower than wild-type). From these observations, we believe that RhoNUC represents a newly identified class of proteins exhibiting both a cellular signalling function (G-protein activity) and a DNA metabolic activity (nuclease activity involved in recombination).
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