Programmed cell death 5 (PDCD5) protein is phylogenetically conserved in both the nucleus and cytoplasm. The human PDCD5 protein is expressed in tumor cells during apoptosis independent of the apoptosis-inducing stimuli, and recently it was found that PDCD5 is an important regulator in both apoptotic and non-apoptotic programmed cell death. In this study, human PDCD5 was expressed in Escherichia coli cell and studied using heteronuclear NMR method. The NMR results indicate that PDCD5 protein call be divided into three Structural re-ions, a core region and two dissociated terminal re ions. The core region (41-101) represents a rigid sub-domain consisting mainly of a triple-helix bundle. The N-terminal 38 residues (3-40) are ordered, but not a rigid Structural region which contains abundant secondary structure, and packs very loosely against the core. The C-terminal 17 residues ( 102-118) represent a mobile unstructured region. which may be capable of interaction with nucleic acid. (C) 2004 Elsevier Inc. All rights reserved.