β-Actin and Nuclear Myosin I are responsible for nucleolar reorganization during DNA Repair

During DNA Repair, ribosomal DNA and RNA polymerase I (rDNA/RNAP1) are reorganized within the nucleolus. Until now, the proteins and the molecular mechanism governing this reorganisation remained unknown.Here we show that Nuclear Myosin I (NMI) and Nuclear Beta Actin (ACTβ) are essential for the proper reorganisation of the nucleolus, after completion of the DNA Repair reaction.In NMI and ACTβ depleted cells, the rDNA/RNAP1 complex can be displaced at the periphery of the nucleolus after DNA damage but cannot re-enter within the nucleolus after completion of the DNA Repair. Both proteins act concertedly in this process. NMI binds the damaged rDNA at the periphery of the nucleolus, while ACTβ brings the rDNA back within the nucleolus after DNA repair completion. Our results reveal a previously unidentified function for NMI and ACTβ and disclose how these two proteins work in coordination to re-establish the proper rDNA position after DNA repair.