Plays a role in the cellular response to DNA damage and the maintenance of genome stability through its association with the MRN damage-sensing complex. Promotes chromatin loading and activity of the MRN complex to facilitate subsequent ATM-mediated DNA damage response signaling and DNA repair. Associates with the MRE11-RAD50-NBN (MRN) damage-sensing complex; this association is constitutive. Interacts with MRE11. Interacts with NBN. Interacts with RAD50. Recruited to sites of DNA damage. Phosphorylation on Ser-115 induces its nuclear localization and promotes genome stability. Phosphorylated; phosphorylation is constitutive and occurs in the absence of any DNA-damaging stimulus. Phosphorylation on Ser-115 is necessary for its nuclear retention. Belongs to the MRNIP family.