Structural mapping of spliceosomes by electron microscopy.

Eukaryotic genes are transcribed as pre-mRNAs which are interrupted by noncoding introns. Selection and accurate removal of introns is an essential step in gene expression that is performed by a large and highly dynamic macromolecular machine, called spliceosome. A major challenge for structural studies of the spliceosome is represented by its large size as well as its dynamic nature. Electron microscopy is an important technique to study the overall shape and architecture of spliceosomes and their components, and to locate subunits and RNA parts. Recent advances in sample preparation of spliceosomes, technical improvements in EM instrumentation, powerful computer hardware, and new image analysis software will be instrumental to push structural studies of spliceosomes to a higher level of resolution.