Systemic destruction

Cristae in crisis ristae, the complex involutions of the mitochondrial inner membrane, vastly increase the surface area across which ATP synthase can generate a proton gradient. Now, new findings from Jean Velours (Université Victor Ségalen, Bordeaux, France) and colleagues suggest that ATP synthase may be important in forming cristae in the first place. Velours' theory is that oligomerization of ATP synthase in the mitochondrial inner membrane helps tubulate the membrane. This idea was first suggested based on the zippered rows of ATP synthase molecules visible on the cristae of Paramecium mitochondria. Velours does not yet know if yeast has the same arrangement. But in the new work he detects the formation of yeast ATP synthase oligomers biochemically. Loss of the nonessential e or g subunits of ATP synthase both disrupts oligomerization and results in mitochondria that lack conventional cristae. The mutant mitochondria have an inner membrane that is wound around itself in an onion shape. The new evidence provides only a correlation between oligomerization and cristae formation, but Velours is now planning more direct electron microscopy experiments to see if oligomerization is indeed responsible for curving the membrane into cristae. ᭿ C Mitochondrial cristae (top) turn onion shaped in the absence of an ATP synthase subunit (bottom). transmembrane protein identified by Craig Hunter and colleagues (Harvard University) may act as a channel that allows an RNAi signal to spread throughout a worm's body and, perhaps, even a mouse or human body. RNAi may target the double-stranded RNA (dsRNA) forms of invading viruses or mobile transposons, but in the laboratory dsRNA is used to trigger the destruction of mRNAs with the same sequence. In worms and, in a similar process, in plants, the destruction spreads systemically. " This systemic effect greatly simplifies the use of RNAi as a genetic tool, " says Hunter, as worms can even be treated by soaking them in a solution of dsRNA. " But nobody has addressed it experimentally to discover how it works. " Hunter set out to find mutants that could still do localized RNAi, in cells expressing both a dsRNA and a corresponding target gene, but could no longer spread that RNAi signal to other cells expressing only the target gene. One of the three genes that he found, called sid-1 , encodes a protein with 11 predicted transmembrane domains. There are homologues in mice and humans and " the strongest homology is …