RDM1 (RAD52 Motif 1) is a vertebrate protein involved in the cellular response to the anti-cancer drug cisplatin. In addition to an RNA recognition motif. RDM1 contains a small amino acid motif, named RD motif, which it shares with the recombination and repair protein, RAD52. RDM1 binds to single- and double-stranded DNA, and recognizes DNA distortions induced by cisplatin adducts ill vitro. Here, we have performed all in-depth analysis of the nucleic acid-binding properties of RDM1 using gel-shift assays and electron microscopy. We show that RDM1 possesses acidic pH-dependent DNA-binding activity and that it binds RNA as well as DNA, and we present evidence from competition gel-shift experiments that RDM1 may be capable of discrimination between the two nucleic acids. Based on reported studies of RAD52, we have generated an RDM1 variant mutated in its RD motif. We find that the L(119)GF -> AAA mutation affects the mode of RDM1 binding to single-stranded DNA. (c) 2006 Elsevier Inc. All rights reserved.