In some of the smallest motion systems in nature, scientists are now identifying how viruses sweep material inward. This artist's conception depicts the structure of one “molecular motor” that packages DNA into the head segment of the T4 virus — here, shown in cross section. Researchers at Purdue University and The Catholic University of America have determined the atomic structure of this motor, which is made of two ringlike structures. The hands in the image represent the five segments of the ringlike structures; each hand takes a turn grabbing the DNA and moving it into the head until it is full.