Decapping and decay of messenger RNA (mRNA) occur in cytoplasmic processing bodies (P bodies) in yeast. The study shows that proteins involved in mRNA decapping and degradation are concentrated in P bodies. These foci are dynamic and their size and number are affected by the rate of mRNA decay. Decapping is a key step in mRNA turnover, allowing 5' to 3' exonucleolytic decay. The study also shows that mRNA degradation intermediates are localized to P bodies, suggesting that these structures are sites of mRNA decay. The results indicate that P bodies are sites of mRNA decapping and 5' to 3' exonucleolytic decay, and that the size of P bodies reflects the flux of mRNAs undergoing decapping. The study also shows that P bodies may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The findings suggest that P bodies are dynamic sites of mRNA metabolism and may play a role in the regulation of mRNA degradation. The study also shows that P bodies are present in mammalian cells, suggesting that equivalent structures may exist in higher eukaryotes. The study provides evidence that P bodies are sites of mRNA decay and that they may be involved in the regulation of mRNA metabolism. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The study suggests that P bodies are important sites of mRNA metabolism and that they may play a role in the regulation of mRNA degradation. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The study provides evidence that P bodies are sites of mRNA decay and that they may be involved in the regulation of mRNA metabolism. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation.Decapping and decay of messenger RNA (mRNA) occur in cytoplasmic processing bodies (P bodies) in yeast. The study shows that proteins involved in mRNA decapping and degradation are concentrated in P bodies. These foci are dynamic and their size and number are affected by the rate of mRNA decay. Decapping is a key step in mRNA turnover, allowing 5' to 3' exonucleolytic decay. The study also shows that mRNA degradation intermediates are localized to P bodies, suggesting that these structures are sites of mRNA decay. The results indicate that P bodies are sites of mRNA decapping and 5' to 3' exonucleolytic decay, and that the size of P bodies reflects the flux of mRNAs undergoing decapping. The study also shows that P bodies may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The findings suggest that P bodies are dynamic sites of mRNA metabolism and may play a role in the regulation of mRNA degradation. The study also shows that P bodies are present in mammalian cells, suggesting that equivalent structures may exist in higher eukaryotes. The study provides evidence that P bodies are sites of mRNA decay and that they may be involved in the regulation of mRNA metabolism. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The study suggests that P bodies are important sites of mRNA metabolism and that they may play a role in the regulation of mRNA degradation. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation. The study provides evidence that P bodies are sites of mRNA decay and that they may be involved in the regulation of mRNA metabolism. The study also shows that P bodies are dynamic structures that may be involved in the storage of mRNA decay factors and that they may function as specific sites for mRNA degradation.