Role of the nuclear matrix protein C1D in regulation of transcription

The nuclear matrix protein C1D is an activator of DNA-dependent protein kinase (DNAPK), which is involved in non-homologous end joining and V(D)J recombination. Moreover, the nuclear matrix proteins C1D was shown to be phosphorylated in vitro by DNA-PK and its mRNA and protein levels have been demonstrated to be induced upon γ-irradiation. The available information suggests that C1D may play a role in DNA DSB-response pathways by targeting DNAPKcs to nuclear matrix and matrix-associated DNA where DNA-PK may regulate several cellular processes. In an attempt to identify the biological function of C1D, the yeast two-hybrid system was employed and C1D was found to interact with a partial clone of TAFI 48, which is a subunit of the promoter selectivity factor SL1 required for the accurate initiation of transcription from the human ribosomal promoter. The possibility of an interaction between C1D and TAFI 48 was potentially important as DNA-PK was found to be capable of repressing Polymerase I transcription in vitro. In this study, it was shown that C1D and TAFI 48 interact specifically in yeast, in vitro and in mammalian cells. It ıs belıeved that this interaction could have potential roles in regulating the repression of transcription from rDNA by DNA-PK in response to DNA double-strand breaks.