RESUMEN
Mutation of the Saccharomyces cerevisiae RAD52 epistasis group gene, MRE11, blocks meiotic recombination, confers profound sensitivity to double-strand break damage, and has a hyperrecombinational phenotype in mitotic cells. We isolated a highly conserved human MRE11 homologue using a two-hybrid screen for DNA ligase I-interacting proteins. Human MRE11 shares approximately 50% identity with its yeast counterpart over the N-terminal half of the protein. MRE11 is expressed at the highest levels in proliferating tissues, but is also observed in other tissues. The MRE11 locus maps to human chromosome 11q21 in a region frequently associated with cancer-related chromosomal abnormalities. A MRE11-related locus was found on chromosome 7q11.2-q11.3.
Asunto(s)
Cromosomas Humanos Par 11 , Cromosomas Humanos Par 7 , Endodesoxirribonucleasas , Exodesoxirribonucleasas , Proteínas Fúngicas/genética , Hominidae/genética , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Secuencia de Aminoácidos , Animales , Aberraciones Cromosómicas , Bandeo Cromosómico , Trastornos de los Cromosomas , Mapeo Cromosómico , Reparación del ADN , Proteínas de Unión al ADN/genética , Proteínas Fúngicas/biosíntesis , Expresión Génica , Biblioteca de Genes , Genes Fúngicos , Humanos , Hibridación Fluorescente in Situ , Cariotipificación , Datos de Secuencia Molecular , Neoplasias/genética , Proteína Recombinante y Reparadora de ADN Rad52 , Homología de Secuencia de Aminoácido , Transcripción GenéticaRESUMEN
Bloom syndrome and a clinically related syndrome represented by the cell line 46BR have been associated with reduction in DNA ligase I activity. In these syndromes, DNA ligase I deficiency severely impairs the development and function of the immune system. We undertook analysis of DNA ligase I-deficient cells to determine whether the observed immune deficiency is attributable to a perturbation in the process of V(D)J recombination. V(D)J recombination in Bloom syndrome cell lines and 46BR was examined by a transient transfection assay. No effect on the fidelity of coding and signal junction formation in DNA ligase I-deficient cells was observed. The frequency of V(D)J recombination in DNA ligase I-deficient cells was also examined using recombination substrates modified to function in human cells. Similar recombination frequencies were observed in normal and DNA ligase I-deficient cells, demonstrating that the efficiency of the V(D)J recombination process is unaffected by alterations in DNA ligase I activity. Rearranged immunoglobulin loci from Bloom syndrome cell lines and patient material were molecularly cloned by an inverse polymerase chain reaction strategy which should be applicable to a variety of human immunodeficiency syndromes and were indistinguishable from those found in normal bone marrow samples. Our data argue that the immune system defects associated with DNA ligase I deficiency do not result from perturbation of the V(D)J recombination pathway.