FACT is a vital protein which has multiple roles including one in transcription and repair of damaged DNA. However, how FACT assists repair and transcription remains elusive. In this work, we have first studied the role of FACT in Base Excision Repair (BER). We used nucleosomes containing DNA with randomly incorporated uracil. We found that the enzyme UDG is able to remove uracils facing the solution and not the uracils facing the histone octamer. The simultaneous presence of FACT and RSC (a chromatin remodeler involved in repair) allows, however, a very efficient removal of uracil facing the histone octamer by UDG. In addition, the concerted action of FACT and RSC permits the removal of the otherwise un-accessible oxidative lesion 8-oxoG from nucleosomal templates by OGG1. This was achieved thanks to the co-remodeling activity of FACT. Here we described for the first time this novel property of FACT and we show in a series of biochemical experiments that FACT is able to boost the remodeling activity of RSC. The experiments reveal that the presence of FACT increases the efficiency of RSC to transform the energy freed by ATP hydrolysis into “mechanical” work. The presented data suggest a stochastic nature of BER functioning in vivo, FACT being a key factor in the repair process. The implication of the co-remodeling activity of FACT in NF-kB factor binding to nucleosomal templates was also investigated. The generation of remodeled, but not mobilized nucleosomes (remosomes), was not sufficient to promote NF-kB binding. However, the RSC-induced nucleosome mobilization allows efficient NF-kB interaction with nucleosomal DNA. Our data are instrumental in deciphering the molecular mechanism of FACT implication in BER and NF-kB mediated transcription.
