Figure 4

Neighbor-joining tree for ORC and Cdc6 proteins. Orc1-5 and Cdc6 sequences were retrieved from the NCBI protein database for H. sapiens (Hs), X. laevis (Xl), D. melanogaster (Dm), S. cerevisiae (Sc), and S. pombe (Sp). The protein corresponding to Cdc6 in S. pombe is named Cdc18 in this species. AAA+ domain regions were extracted from Orc1-5 and Cdc6 sequences using the Walker A and Walker B motifs identified in [19]. The multiple sequence alignment program Muscle [81] was used to align the sequences, and any regions in the multiple sequence alignment containing gaps were deleted. The resulting ungapped alignment was used to construct a phylogenetic tree using the BioNJ algorithm [82]. One hundred resampled alignments were used to generate bootstrap values, with values greater than 70% indicated. For the five eukaryotic organisms from yeast to human, the Orc1-5 and Cdc6 sequences are conserved across all organisms. Orc1 seems to be the most highly conserved, and Orc3 the most divergent, within a group. Interestingly, Orc1 is most closely related to Cdc6 within the ORC-Cdc6 family. Orc6 was not aligned, as it does not share the AAA+ domain with the other members. Scale bar represents changes per site.