Figure 2.

SMN self-association specifically increases the binding affinity for Sm proteins. (a) GST or GST-SMN was preincubated with or without a 4-fold molar excess of His-SMN as described in Materials and Methods. After washing away unbound His-SMN, in vitro translated [³⁵S]methionine-labeled SMN, SmB, or SIP1 was added and the binding assay was performed as described in Materials and Methods. Bound proteins were analyzed by SDS/PAGE and fluorography. The in vitro translation area shows 10% of the input. (b) GST-SMN was preincubated with or without a 4-fold molar excess of His-SMN as described above. In vitro translated [³⁵S]methionine-labeled Sm proteins then were added, and the binding assay was performed as described in Materials and Methods. The in vitro translation area shows 25% of the input.