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How do cells track down the occasional lesion among the billons of base pairs of chromosomal DNA? A surprising discovery unravels a potential new mechanism: the Tudor domains of the DNA-damage response factor 53BP1 interact with methylated histones that are likely to become exposed during local chromatin relaxation at sites of DNA double-strand breaks.
Formins are a family of structurally conserved proteins that regulate the assembly of the fast-growing end of actin filaments. New work shows that the molecular mechanism of formin function is conserved but that the rates of the reactions vary within and between species to such a degree that the mechanisms of various formin family members may seem to differ qualitatively.
The finding that Eps8 caps the barbed ends of actin filaments adds to the growing list of factors responsible for controlling the dynamics of actin polymerization. The requirements for these capping proteins may vary in each cellular context, but EPS-8 seems to be critical during intestinal morphogenesis in the worm.
The cell cycle regulator p27Kip1 must be degraded to permit cell division. Degradation is moderate in G1 phase, but is enhanced in S-phase. Now, a novel ubiquitin ligase that can ubiquitinate p27 leading to its proteolysis after mitogen stimulation has been identified.
Growing evidence suggests that semaphorins — known to provide directional cues during axon guidance — also provide regulatory signals for cell migration during tissue morphogenesis. During heart development, it is crucial that semaphorins can signal bidirectionally, functioning as both a ligand and a receptor. Through these distinct signalling pathways, semaphorins can provide both 'stop' and 'go' signals for cell motility and invasive growth.
Over more than three decades, sporadic and circumstantial evidence has accumulated to suggest that nuclear actin has crucial functions in RNA polymerase II-based transcription. Now, using a biochemical approach, β-actin has been identified as a highly specific, constitutive component of the active transcriptional complex required for formation of the pre-initiation transcription complex.
The MRL protein family is emerging as a new connection between signalling, adhesion and cell motility. Two members, lamellipodin and RIAM, can regulate both actin assembly and cell adhesion, which raises many questions about how their interactions with Ena/VASP proteins, Ras-related GTPases and membranes orchestrate these key processes.
Microtubule-mediated transport is essential for neuronal viability, neurite extension, synapse formation and synaptic function. Now a new kinesin receptor, syntabulin, has been identified that controls transport of the t-SNARE syntaxin along microtubules.