In human genes, protein-coding regions alternate with non-coding “introns” that must be snipped out of the RNA transcript before it is used to produce a protein. The snipping is done by the spliceosome, a complex molecular machine that must assemble anew on each intron it removes.  The spliceosome must cut out exactly the segments of the messenger molecule that require removal, no more and no less, since inaccurate intron removal can produce a messenger molecule that is non-functional or that causes disease.

To help understand how multiple introns are quickly and accurately removed, postdoctoral fellow Joerg Braun developed a light microscopy method by which for the first time we can observe the coordinated processes by which human spliceosomes recognize and assemble around the segments of single messenger RNA molecules.  As the eLife digest puts it: “The experiments show that spliceosomes working on different introns in the same pre-mRNA actually help each other out. As one assembles, this helps the spliceosome that processes the neighboring intron to get built. In particular, the U1snRNPs [a spliceosome sub-assembly] processing nearby introns collaborate to promote the assembly and activity of the spliceosomes. This teamwork is likely important to guarantee that multiple introns are cut out quickly and accurately.”