Reviews & Analysis

Most kinesins move processively along microtubules using energy derived from ATP hydrolysis. Almost all of the intermediate structures of this ATPase reaction cycle have been solved for the monomeric kinesin 3 family motor KIF1A. These structures suggest that kinesins might move by a common mechanism.

During cell division, the asymmetric localization of epigenetic marks and kinetochore proteins might lead to the differential recognition of sister chromatids and the biased segregation of DNA strands to daughter cells. This might ultimately result in the acquisition of distinct cell fates after mitosis.

The reconstitution of biological processes from purified components is a powerful approach to understanding the principles that govern cellular organization. The recent development of new experimental techniques is enabling the reconstitution of increasingly complex cellular systems.

The growth of microtubules is accompanied by large fluctuations in rates and abrupt transitions between phases of growth and shrinkage. The authors propose that fluctuations in the length of the GTP–tubulin cap at the microtubule end could be the main source of variation.

In interphase, chromosomes are associated with proteins and RNAs that participate in many metabolic processes. During mitosis, these components might inhibit chromosome segregation or reduce its fidelity. The author proposes the existence of a molecular mechanism that eliminates unwanted components from mitotic chromosomes.

Compositionally and functionally distinct RNA granules are found in the cytoplasm of somatic and germ cells. The components of most RNA granules are in a dynamic equilibrium, thereby allowing rapid shifts between the translation, storage and decay of RNAs.

Protein sumoylation affects many biological processes, but it was not previously thought to target proteins for degradation. Recent findings unravel a new role for small ubiquitin-like modifier (SUMO) as a signal for the recruitment of ubiquitin ligases, which leads to protein ubiquitylation and degradation.

Guanine nucleotide-binding (G) proteins are regulated by GTPase-activating proteins and guanine nucleotide-exchange factors. Another class of G proteins is emerging that are regulated by homodimerization. The authors propose that juxtaposition of the G domains of two monomers across the GTP-binding sites activates the biological function of these proteins and the GTPase reaction.

The uropod, a protrusion at the rear of amoeboid motile cells such as leukocytes, exemplifies the importance of morphology in cell motility. Although the signalling and structural requirements of uropod formation are being characterized, a clear understanding of uropod function is still lacking.

Coat proteins, such as coat protein I (COPI), couple vesicle formation with cargo sorting to ensure the generation of correctly packaged transport vesicles. Emerging evidence suggests that some long-held views on how COPI vesicles are formed need to be revised.

Endosomes have important roles in processes, including cytokinesis, polarization and migration, in which their function might be distinct from those classically associated with endosomes. We speculate that endosomes function as multifunctional platforms on which unique sets of molecular machines are assembled to suit different cellular roles.

Myofibril assembly results in an array of identical sarcomeres in striated muscle. Recent studies have begun to unravel the mechanisms that set sarcomere spacing and the assembly of initial sarcomere arrays, and point to integrin-dependent adhesion as the starting point for myofibrillogenesis.

Maintenance of organ homeostasis and control of appropriate responses to environmental alterations requires the coordination of cellular functions and tissue organization. This coordination could be achieved by proteins that can have distinct but linked functions on both sides of the plasma membrane.

General principles that govern how microRNAs select their targets and determine their mode of action are being challenged by recent findings in plant and animal systems. A common shortcoming of studies to date has been to address these questions under truein vivoconditions.

Mechanical forces that are exerted on surface-adhesion receptors can be channelled along cytoskeletal filaments and concentrated at distant sites in the cytoplasm and nucleus. How do these forces act at a distance to induce mechanochemical conversion in the nucleus, and what effects can they have on the cell?