P-bodies and stress granules: possible roles in the control of translation and mRNA degradation

Abstract

The control of translation and mRNA degradation is important in the regulation of eukaryotic gene expression. In general, translation and steps in the major pathway of mRNA decay are in competition with each other. mRNAs that are not engaged in translation can aggregate into cytoplasmic mRNP granules referred to as processing bodies (P-bodies) and stress granules, which are related to mRNP particles that control translation in early development and neurons. Analyses of P-bodies and stress granules suggest a dynamic process, referred to as the mRNA Cycle, wherein mRNPs can move between polysomes, P-bodies and stress granules although the functional roles of mRNP assembly into higher order structures remain poorly understood. In this article, we review what is known about the coupling of translation and mRNA degradation, the properties of P-bodies and stress granules, and how assembly of mRNPs into larger structures might influence cellular function.

Figure 1.

Eukaryotic mRNA decay pathways. (A) General mRNA decay pathways. (B) Specialized decay pathways that degrade translationally aberrant mRNAs.

Figure 2.

Model for P-body assembly in yeast. First, P-body factors are recruited to the mRNA as complexes. Second, interactions between P-body proteins in the complexes lead to the formation of a “closed-loop” structure. Finally, mRNPs aggregate via the Q/N domain of Lsm4, the Yjef-N domain of Edc3, or the amino-terminal domain of Pat1 to form microscopically visible cytoplasmic granules.

Figure 3.

Model of the “mRNA cycle.” Showing the dynamic movement of mRNA between polysomes, P-bodies, and stress granules, and the possible mRNP transitions between the different states of the mRNA.