Poly(A)-specific ribonuclease (PARN), a key enzyme involved in eukaryotic mRNA decay, contains one catalytic domain and two RNA-binding domains. Here we found that at least one RNA-binding domain is required for the substrate binding, but not for the catalysis of PARN. The removal of the R3H domain led to a dramatic decrease in PARN stability and a change in the aggregation kinetic regime, while only minor effects were observed for the removal of the RRM domain or both RNA-binding domains. Thus the R3H domain might stabilize PARN by acting as a protector or intermolecular chaperone of the RRM domain. (c) 2007 Elsevier Inc. All rights reserved.