Sorting the mRNA overflow

Selected mRNAs and their bound proteins are passed from stress granules (SGs) to processing bodies (PBs), according to evidence presented by Kedersha et al. (page 871). The group suggests that SGs hold and sort the overflow from the translational apparatus, some of which is subsequently sent to PBs for degradation.

Stresses such as heat shock induce the cytoplasmic appearance of SGs—aggregates of mRNAs that are redirected from polysomes when translation initiation is blocked. The new results show that components of SGs sometimes flow to sites of mRNA degradation called PBs. Other proteins are found only at SGs, such as eIF3 and poly(A)-binding proteins, or only at PBs, such as decapping enzymes.

SGs and PBs formed independently—mild heat shock induced only SGs, and PBs formed even in mutant cells in which...