Single-particle electron cryomicroscopy recently helped a group of researchers to capture a 4.5-Å-resolution 3-D image of the capsid of ε15, a double-stranded DNA bacteriophage — a virus that infects bacteria.Wen Jiang from Purdue University in West Lafayette, Ind., and Matthew L. Baker from Baylor College of Medicine in Houston, led the group, which also included members from MIT in Cambridge, Mass. The image of the 22-MDa structure provided enough details to trace the polypeptide chain (see figure). This information could reveal how the proteins in the capsid perform biological tasks, which could help clinicians who are developing disease treatments. The work was published in the Feb. 28 issue of Nature.Electron cryomicroscopy can image viruses as they exist in nature rather than in the form required for x-ray crystallography. Crystallization can be challenging or even impossible — the latter being the case for double-stranded DNA bacteriophages thus far.The researchers have the goal of reaching 3- to 4-Å resolution, which would allow them to see the amino acids. In addition, they plan to keep refining the techniques and to examine more medically relevant virus species.