Co-affinity precipitation SF (Strep-Flag)-tagged protein was precipitated with Strep-Tactin magnetic beads (Qiagen). 293 cells were first infected with rMP-12 tagged with SF-tag (moi 3) and were then transfected with in vitro synthesized capped RNA (encoding NSD6-30, NSD31-55, NSD56-80, NSD81-105, NSD106-130, NSD131-155, NSD156-180, NSD181-205, NSD206-230, NSD231-248, or NSD249-265). After incubation for 6 hours, newly synthesized proteins were then labeled with [ 35 S] methionine/cysteine (MP Biomedicals). Using cell lysates, SF-tagged proteins were precipitated with Strep-Tactin beads according to manufacturer's instructions. Then, co-precipitated proteins were analyzed by separating on 10% SDS-PAGE gel and followed by autoradiography.