A new view of translational control: how P-bodies, stress granules, and other cytoplasmic foci manage the cellular currency.

The bank note that Dominique Weil used to buy ice cream for her family at the beach this past summer may have traveled a long way. The note, a product of international treaties and detailed artistry, could have crossed a dozen international borders or more. Complicated decisions from individual consumers to corporate accountants and government agencies determined its path from bank to pocket to cash register and back--possibly saved for days or years in case of a rainy day. After getting too old, worn, or torn, treasury inspectors may destroy and replace the note. Or if inflation is too high, it could be removed from circulation altogether.

Organized distribution is crucial to smooth operation in everything from economies to trash disposal. When efficiently optimized, such systems borrow from a logic as simple as that of the assembly line: Concentrate the right resources in the right places. Local, specialized processing centers should recycle where possible, prepare for emergencies, and dispose of waste promptly. Why would anyone expect something as elegant as a cell to act any differently?

RNA FROM MINT TO CIRCULATION

Yet as recently as 15 years ago, researchers viewed the nucleus as just "a bag of goo," with a disorganized, free-floating genome, says Greg Hannon of Cold Spring Harbor Laboratory in New York. Fluorescent tags and electron microscopy have since revealed how membraneless structures organize nucleic-acid metabolism. High concentrations of RNA polymerases appear in anywhere between 500 and 10,000 nuclear loci. Elsewhere in the nucleus, dozens of splicing speckles aggregate pre-mRNA transcripts and splicing factors, playing their part in the assembly line of posttranscriptional modification.

But after transcripts are spliced, capped, polyadenylated, and ejected through the nuclear pore, "the trail goes cold," says Kenneth Kosik of the University of…