We generated a genome-wide replication profile in the genome of Lachancea 
kluyveri and assessed the relationship between replication and base composition. 
This species diverged from Saccharomyces cerevisiae before the ancestral whole 
genome duplication. The genome comprises eight chromosomes among which a 
chromosomal arm of 1 Mb has a G + C-content much higher than the rest of the 
genome. We identified 252 active replication origins in L. kluyveri and found 
considerable divergence in origin location with S. cerevisiae and with Lachancea 
waltii. Although some global features of S. cerevisiae replication are 
conserved: Centromeres replicate early, whereas telomeres replicate late, we 
found that replication origins both in L. kluyveri and L. waltii do not behave 
as evolutionary fragile sites. In L. kluyveri, replication timing along 
chromosomes alternates between regions of early and late activating origins, 
except for the 1 Mb GC-rich chromosomal arm. This chromosomal arm contains an 
origin consensus motif different from other chromosomes and is replicated early 
during S-phase. We showed that precocious replication results from the specific 
absence of late firing origins in this chromosomal arm. In addition, we found a 
correlation between GC-content and distance from replication origins as well as 
a lack of replication-associated compositional skew between leading and lagging 
strands specifically in this GC-rich chromosomal arm. These findings suggest 
that the unusual base composition in the genome of L. kluyveri could be linked 
to replication.