Figure 4.

Mg²⁺ and ATP requirements for homologous pairing by Xrcc3⋅Rad51C. (A) Mg²⁺ dependence of homologous pairing by Xrcc3⋅Rad51C. A ³²P-labeled single-stranded 120-mer oligonucleotide (1.6 μM) was incubated with Xrcc3⋅Rad51C (0.5 μM) at 37°C for 5 min in the presence of various amounts of MgCl₂. The reactions were initiated by the addition of pGsat4 form I DNA (13 μM) and were continued for 10 min. MgCl₂ concentrations are 0 mM (lane 1), 1.25 mM (lane 2), 6.25 mM (lane 3), 13 mM (lane 4), 26 mM (lane 5), and 50 mM (lane 6). (B) ATP dependence of homologous pairing by Xrcc3⋅Rad51C. A ³²P-labeled single-stranded 120-mer oligonucleotide (1.6 μM) was incubated with RecA (0.1 μM) or Xrcc3⋅Rad51C (0.5 μM) at 37°C for 5 min in the presence or absence of ATP, and the reactions were initiated by the addition of 12 mM MgCl₂ and pGsat4 form I DNA (13 μM). Lanes 1–3 are reactions with ATP, and lanes 4–6 are reactions without ATP. Lanes 1 and 4 are negative controls without protein. Lanes 2 and 5 are the reactions with RecA, and lanes 3 and 6 are the reactions with Xrcc3⋅Rad51C.