To identify proteins that interact with human METTL2A or 2B, we generated 293T human embryonic cell lines stably expressing METTL2A or METTL2B fused to the Twin-Strep purification tag35. As a comparison, we also generated a 293T cell line stably expressing Strep-tagged METTL6, a different human Trm140 homolog. Strep-METTL2A, METTL2B and METTL6 were affinity purified from whole cell extracts on streptactin resin, eluted with biotin and analyzed by silver staining to detect interacting proteins. We identified a closely-migrating doublet of bands at ~50 kDa along with a band at ~30 kDa that were enriched with METTL2A and METTL2B compared to the control purification (Fig. 1a, arrowheads). Immunoblotting with anti-Strep tag antibodies revealed that one of the 50 kDa bands was purified Strep-METTL2A/B (Supplementary Fig. 1). The METTL6 purification yielded bands at ~60, 40, and 30 kDa (Fig. 1a, arrowheads). The 40 kDa band corresponds to purified Strep-METTL6 as detected by immunoblotting with anti-Strep tag antibodies (Supplementary Fig. 1).
