in model organisms, MCM10 is required for forming the pre-initiation complex for initiation of chromosome replication and is involved in the elongation step. To investigate the role of MCM10 in human chromosome replication, we used small interfering RNA (siRNA) in MCM10-knockdown experiments and found that knockdown accumulated S and G2 phase cells. The chromosome replication of MCM10-knockdown cells was slowed during early and mid S phases, although Cdc45, Pol alpha, and PCNA proteins were loaded onto the chromatin, and was aberrant during late S phase. Our results indicate that MCM10 is essential for the efficient elongation step of chromosome replication. (C) 2007 Elsevier Inc. All rights reserved.