We previously reported not only that chicken HIRA, a homolog of Saccharomyces cerevisiae transcriptional corepressors Hir1p and Hir2p, possesses seven WD dipeptide motifs and a LXXLL motif in its N-terminal half and C-terminal half, respectively, but also that the N-terminal and C-terminal halves, respectively, bind to CAF-1p48 and HDAC-1 and -2 in vitro. Seven WD dipeptide motifs in the N-terminal half of HIRA are required for the in vitro interaction with CAF-1p48. The LXXLL motif at positions 993997 of HIRA is necessary for the in vitro interaction with HDAC-2. Here we revealed not only that the N-terminal and C-terminal halves of HIRA mediate individually transcription repressions but also that even one of the seven WD dipeptide motifs and the LXXLL motif of HIRA are essential for the mediations in vivo. Moreover, the LXXLL motif is essential for the interaction with endogenous or recombinant HDAC-2 in vivo, probably resulting in formation of the active complex, harboring the HDAC activity. Taken together, these results indicate that HIRA should participate differentially in a number of DNA-utilizing processes, including transcription repressions, through interactions of its distinct regions with CAF-1p48 and HDAC-2, respectively. (C) 2003 Elsevier Inc. All rights reserved.