Analysis of the function of the nuclear matrix-associated protein C1D

Abstract

DNA Double-strand breaks (DSBs) are generated as intermediate stnictures during V(D)J recombination, as a consequence of oxidative metabolism, or can be induced by exogenous factors such as gamma irradiation and radiomimetic drugs. Mutational studies identified the serine/threonine kinase, DNA-PK, as an essential component of DNA DSB repair machinery. The activation of the multi-component DNA-PK complex requires either free DNA ends or an association with the nuclear-matrix associated protein CID, which facilitates the activation of DNA-PK in a DNA end-independent fashion. The activation of DNA-PK through its interaction with CID, joins an increasing body of evidence which suggests a role for higher order nuclear organisation in the orchestration of complex cellular processes such as transcription, RNA splicing, nucleotide excision repair, replication and double-strand DNA break repair. In this study, the yeast two hybrid system was employed to screen a B-cell cDNA library to identify the interacting proteins with CID, and the interactions determined were further characterised. It was found that, CID interacts specifically with the recombinational hotspot binding protein Translin and Translin associated factor X, TRAX, both in vitro and in vivo, providing evidence that C 1D may play a critical role in DNA repair and recombination. Interestingly, an interaction between TRAX and DNAPKcs has also been identified under in vivo conditions. Tlie interaction of TRAX with DNA-PKcs and C ID indicates a connection between DNA double-strand break repair, recombination, and dynamic nuclear architecture.