Single particle electron microscopy reconstruction can be a powerful tool for determining the structure of large protein complexes. One limitation of the technique is the difficulty in coming up with specific labels for the protein that can be visualized with EM. In a new paper in RNA, postdoc Beth Stroupe and coworkers show that the use of the actin-nucleating protein Spire as a cloneable tag allows them to nucleate actin filaments that then “point” to the location of the tag in the complex seen in EM, and applied the technique to their studies of the C complex spliceosome.
