Figure 4. Assay of DNA binding activity of wild-type phi C31 integrase.

A fixed amount (16 fmol) of a 41 bp biotin -labeled attB fragment (A) or a 50 bp biotin -labeled attP fragment(B) was incubated with varying amounts of purified wild -type phi C31 in binding buffer at 30°C for 30 min. Reactions were analyzed by polyacrylamide gel electrophoresis (5% polyacrylamide, 1x Tris-borate-EDTA). Arrows show the positions of free probe (F) and the DNA binding complexes (I, II and III).