Figure 3.

Dynamics of ORF1p-ssDNA compaction at low, fixed extension. (A) ssDNA previously incubated for 100 seconds at 30 pN with 30 nM 111p was held at a minimal, fixed extension (∼0.2 nm/nt) in protein-free buffer for 2 minutes. The protein–ssDNA complex was then stretched until reaching a tension of 75 pN (1), where it was held for 100 s (2). Tension on the strand was then released by reducing its extension to the initial value (3). (B) Incubation of the complexes formed by 111p in protein-free buffer at low extension (0.2 nm/nt) was repeated for 5, 15 or 30 min. The ssDNA extension for both the initial stretch (closed circles) and subsequent release (open circles) is inversely proportional to the initial incubation time. (C) Extension of the pre-formed ssDNA–ORF1p complex at 30 pN during stretching (normalized to the length of protein-free ssDNA) shows that the compaction of the active protein–DNA complexes (111p and m14) is greater than that of the inactive proteins (151p and m15). (D) Similarly, during release, the reduction of extension at 30 pN is greater for the active proteins than the inactive variants.