Repressor specific for genes preceded by a radiation/desiccation response motif (RDRM) site, which is present upstream of several radiation-induced genes. Forms at least dimers. Interacts with IrrE. Cleaved between Leu-106 and Arg-107 by the IrrE metalloprotease after exposure to radiation. Cleavage inactivates DdrOC, leading to derepression of the target genes.