Model showing the role of EE motility in polysome distribution. (A) Ribosomal subunits are released from the nucleus, form polysomes on Rrm4-bound mRNA, and get loaded onto EEs that travel through the ribosome subunit–rich region by the activity of kinesin-3 and dynein. Off- and reloading of polysomes from the moving EEs distributes the entire translation machinery in the cell. (B) Ribosome distribution defects in the mutants used in this study. Absence of bidirectional EE motility (No kin3, No dynein), the inability to bind to EEs (No Rrm4), or reduced EE numbers (No Yup1) results in formation of central ribosome subunit clusters.