Fig. 4. UV cross-linking of ATP to BsSMC. BsSMC protein was incubated in a buffer containing 7.5 mM KCl and 2.5 mM MgCl₂ in the presence of [α-³²P]ATP. After incubation at 37°C for 30 min, the sample was irradiated with no UV (lane 1) or UV (lanes 2 and 3) to induce cross-linking in the absence (lanes 1 and 3) or presence (lane 2) of 1 mM non-radioactive ATP. Labeled polypeptides were fractionated by 7.5% SDS–PAGE and visualized by autoradiography.