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In This Issue In This Issue Rabs make their way to mitochondria he large family of Rab GTPases has various functions, including the assembly of proteins required for endocytosis and membrane trafficking. Now, a new function for a Rab is emerging. On page 659, Alto et al. describe a Rab that affects mitochon-drial fission. This GTPase, Rab32, also has an unusual binding partner, the cAMP-dependent kinase PKA. The authors originally sought to identify novel AKAPs, proteins that anchor PKA to subcellular domains. They found Rab32, the first Ras family member GTPase shown to interact directly with PKA. Although a functional connection between the two has yet to be shown, association of the enzymes T Quantity assurance he 2 micron plasmid persists at an optimal copy number of 60 per cell by replicating in conjunction with the host chromosomes only once per cell cycle. This limited replication requires a high fidelity system to divide plasmids evenly between daughter cells. Results from Mehta et al. on page 625 suggest that the plasmid accomplishes this by recruiting a cellular factor used for chromosomal separation. The authors first noticed that mutations that disturb chromosome segregation similarly affect plasmid segregation, so they examined whether proteins involved in sister chromatid pairing also function during plasmid partitioning. They found that a cohesin subunit, Mcd1, was recruited by plasmid proteins Rep1p and Rep2p to a plasmid sequence, STB. STB does not resemble chromosomal cohesin-binding sequences, and cohesin abnormally expressed during G1 was found on STB but not chromosomes. Thus, the plasmid has independently evolved the ability to recruit cohesin. A noncleavable form of cohesin blocked segregation of the plasmids, suggesting that cohesin is used to ensure even partitioning of the plasmids. However, it is also possible that the effect is due to association of the plasmids with missegregating chromosomes, as the Rep proteins were seen in association with chromosomes. Mutations that perturb the ability of plasmids, but not chromosomes, to recruit cohesin should clarify these possibilities. ᭿ T The 2 micron plasmid (green), like chromosomes (top), uses cohesin (orange) to segregate evenly. ells can sense when the pressure is on; they respond to fluid shear stress (FSS) by MAPK activation and reorganization of the actin cytoskeleton, for example. Although signaling cascades controlling these changes are well studied, the molecules that sense mechanical stimuli at the plasma membrane are generally unknown. On page 773, Osawa et al. present strong …