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GFP-tagged Nbs1 dynamically interacts with DNA double strand breaks inflicted by laser microirradiation of a spatially restricted subnuclear volume (yellow stripe; left). In an undamaged cell, GFPNbs1 is distributed throughout the nucleus (right). The image captures live human cells 30 min after laser treatment. Cover design: Lawrence Keogh
The application of modern fluorescence microscopic methods to bacteria has revolutionized our view of their subcellular organization. Many proteins are now known to be targeted with exquisite precision to specific locations in the cell, or to undergo rapid directed changes in localization. Structural and functional homologues of tubulin (FtsZ) and actin (MreB) are now indisputably present in bacteria, overturning the textbook view that the cytoskeleton is unique to eukaryotes. These advances are stimulating a radical rethink about how various fundamental processes are organised in bacteria.
One of the earliest structural changes in cloning by nuclear transfer is the disassembly of the nucleolus. The first insights into the molecular mechanisms of this event have now emerged and the results have tantalising implications for nucleolar architecture.
GTP-binding proteins of the Rho family regulate each other's activities by largely elusive mechanisms. Now, an unexpected signalling pathway has been identified in fibroblasts that links Rac activation to the inhibition of Rho activity, through the release of oxygen radicals.
Separase is a conserved protease that activates the metaphase-to-anaphase transition by cleaving the link between sister chromatids. Furthermore, in Saccharomyces cerevisiae, separase is also involved in promoting mitotic exit through regulating Cdc14 release. A new study now suggests that the mitotic exit function of separase is independent from its protease activity.
The multi-functionality of the adenomatous polyposis coli (APC) tumour suppressor gene keeps surprising cancer molecular biologists. Signal transduction, cytoskeletal organization, chromosomal segregation and cell adhesion are just some of the putative cellular functions previously assigned to this gene and thought to be related to its tumour-suppressing activity. New data on yet another tumour-related function of APC, namely the coordinated regulation of cell adhesion and motility, adds to its host of cellular activities.