Processing bodies require RNA for assembly and contain nontranslating mRNAs

TLDR

Processing bodies (P‑bodies) are cytoplasmic foci enriched in mRNA decay factors, but their physical nature, relationship to translation, and cellular functions remain poorly understood. This study characterizes four properties of yeast P‑bodies that demonstrate they are dynamic, contain non‑translating mRNAs, and participate in stress‑response pathways. The authors show that P‑bodies require RNA for assembly, change in number and size under glucose deprivation, osmotic stress, UV exposure, and growth phase, increase when translation initiation is blocked but dissociate when elongation is inhibited, and lack multiple translation factors and ribosomal proteins, indicating roles beyond mRNA decay.

Abstract

Recent experiments have defined cytoplasmic foci, referred to as processing bodies (P-bodies), wherein mRNA decay factors are concentrated and where mRNA decay can occur. However, the physical nature of P-bodies, their relationship to translation, and possible roles of P-bodies in cellular responses remain unclear. We describe four properties of yeast P-bodies that indicate that P-bodies are dynamic structures that contain nontranslating mRNAs and function during cellular responses to stress. First, in vivo and in vitro analysis indicates that P-bodies are dependent on RNA for their formation. Second, the number and size of P-bodies vary in response to glucose deprivation, osmotic stress, exposure to ultraviolet light, and the stage of cell growth. Third, P-bodies vary with the status of the cellular translation machinery. Inhibition of translation initiation by mutations, or cellular stress, results in increased P-bodies. In contrast, inhibition of translation elongation, thereby trapping the mRNA in polysomes, leads to dissociation of P-bodies. Fourth, multiple translation factors and ribosomal proteins are lacking from P-bodies. These results suggest additional biological roles of P-bodies in addition to being sites of mRNA degradation.