Hexameric complexes of the six related Mcm2-7 proteins form the core of the 
replicative helicase. Two other proteins, Mcm8 and Mcm9, with significant 
homology to Mcm2-7 were first shown to play distinct roles during DNA 
replication in Xenopus laevis egg extract. Recent work has revealed that Mcm8 
and 9 form a complex that plays a role during homologous recombination in human, 
chicken and mouse cells. We have therefore re-examined the behavior of the 
Xenopus homologs of these proteins. We show that Mcm8 and Mcm9 form a dimeric 
complex in Xenopus egg extract. They both associate with chromatin at later 
stages of DNA replication, and this association is stimulated by DNA damage, 
suggesting that their function is analogous to the one described in higher 
eukaryotes. In contrast to previous reports, we do not find Mcm9 essential for 
loading of Mcm2-7 complex onto chromatin during origin licensing nor detect its 
interaction with Cdt1 origin licensing factor. Altogether, we conclude that the 
role Mcm8 and Mcm9 play in Xenopus egg extract is not different from recent 
findings in higher eukaryotes, consistent with an evolutionary conservation of 
their function.