FIG. 8.

Endogenous I3 binds specifically to ssDNA. (A) Comparison of the binding of endogenous and recombinant I3 to ssDNA. Reaction mixtures containing 0.2 pmol of radiolabeled single-stranded 24-mer oligonucleotide and the indicated amounts of either endogenous I3 (VV I3) (lanes 1 to 5) or recombinant I3 (Rec I3) (lanes 6 to 11) were incubated at 30°C for 15 min, fractionated on a 15% nondenaturing polyacrylamide gel at 4°C, and visualized by autoradiography. (B) Comparison of the binding of endogenous I3 to single-stranded and double-stranded DNA. Reaction mixtures contained 0.2 pmol of radiolabeled single-stranded 24-mer oligonucleotide (lanes 1 to 3) or 0.2 pmol radiolabeled double-stranded (ds) 24-mer oligonucleotide (of identical sequence) (lanes 4 to 6) and the indicated amounts of purified endogenous I3. After incubation for 15 min at 30°C, samples were fractionated on a 15% nondenaturing polyacrylamide gel at 4°C and visualized by autoradiography.