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Figure 7.
Figure 7. Cdc6 Domain III(A) Ribbon diagram comparing the
similar regions of Cdc6 domain III (right, gold) and histone H5
(left, blue). “HTH” and “W” designate the
helix-turn-helix and wing regions, respectively.
Secondary-structural elements of Cdc6 correspond to those in
(C).(B) One model for domain III function. Domain III (gold) is
shown docked onto duplex DNA (gray stick). To generate the
model, domain III was superposed on E2F as seen in the E2F/DNA
cocrystal structure ([63]). The rmsd between E2F and P.
aerophilum Cdc6 domain III is 2.4 Å over 64 C[α]
positions. Amino acids known to be important for appropriate
Cdc6 activity are shown as magenta (null mutants) or cyan
(2C-arrest mutants) ball-and-stick. It is interesting to note
that, much like origin sequences, the surface of this domain is
not conserved among Cdc6/Cdc18 orthologs. However, most of the
observed mutations cluster on one side of the domain, and
alleles 46 and 47 fall on or near the putative DNA binding
elements (see Figure 6).(C) ClustalX ([59]) sequence alignment
of the C-termini of Cdc6/Cdc18 and Orc1 orthologs. The
secondary-structural elements observed in Cdc6 are drawn below
as cylinders (α helices), arrows (β strands), and coil
(lines). The P. aerophilum cdc6 and S. pombe cdc18^+ sequences
are boxed in gray, while colors indicate regions of chemical
conservation; for example, blue represents hydrophobic
conservation, orange represents conservation of positively
charged groups, etc.(A) and (B) generated by RIBBONS ([10]).
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