Figure 4 |. Interactions with ubiquitin and DNA.

a, Superposition of the FANCD2^Ub-Ub^I and FANCI^Ub-Ub^D2 interfaces by aligning Ub^D2 (red) with Ub^I (green). The paralogs that each ubiquitin is attached to are not shown for clarity. The ubiquitin hydrophobic patch residues (Leu8, Ile44, and Val70) are shown as sticks for both ubiquitin molecules. Colored as in Fig. 2a. b, Close-up view of the non-covalent interface between FANCD2^Ub (pink) and Ub^I (green) showing the residues within interaction distance as sticks (darker colors). Yellow dotted lines indicate potential hydrogen bonds. c, Close-up view of the reciprocal interface between FANCI^Ub (cyan) and Ub^D2 (green). d, Cartoon, colored as in Fig. 2a, showing ID^Ub side chains within contact distance of the DNA as sticks (darker hues). Gray sticks show the helical axes for the three relatively straight segments of the DNA. The majority of FANCD2^Ub and parts of FANCI^Ub are clipped above the plane of the figure to make the DNA visible (Extended Data Fig. 9f legend lists side chains shown). e, Autoradiogram of DNA binding competition time course after 8 μM of unlabeled 67 bp dsDNA was added to the ID^Ub complex (800 nM) pre-assembled on a 95 bp circular nicked DNA or the corresponding linear nicked DNA, both at 400 nM with only 2 nM of each ³²P labeled. ³²P DNA-protein complexes contain multiple ID^Ub proteins due to the length of each DNA. Fraction of DNA bound is quantified in the chart (repetitions marked by circles, and their mean by a black dash; n=3).