Protein evolution

Components of coated vesicles and nuclear pore complexes share a common molecular architecture. Devos, D. et al. PloS Biol. 2, e380 (2004)

How did the nuclear pore complex (NPC) evolve when prokaryotic organisms lack a comparable transport system? These authors characterized the structures of seven proteins that form a core building block of the NPC, and found that they are structurally similar to protein components of the main types of vesicle-coat complex that maintain vesicle-trafficking pathways. So NPC and coat proteins evolved from an early, common membrane-curving module that led to the development of the complex intracellular membrane system of modern eukaryotes.

Cell fate

A critical role for Cyclin E in cell fate determination in the central nervous system of Drosophila melanogaster. Berger, C. et al. Nature Cell Biol. 5 Dec 2004 (doi:10.1038/ncb1203)

Structural and functional diversity in the central nervous system of Drosophila melanogaster is generated by different cell lineages that arise from some of the serially homologous neuroblasts within the thoracic and abdominal segments. Berger et al. showed that the cell-cycle protein cyclin E is required to specify cell fate in the thoracic neuroblast NB6-4 lineage. It is expressed asymmetrically after the first division of NB6-4t cells and functions upstream of prospero and glial cell missing to generate neuronal cells.

Chromatin

Acetylation by Tip60 is required for selective histone variant exchange at DNA lesions. Kusch et al. Science 4 Nov 2004 (doi:10.1126/science.1103455)

These authors showed that the Drosophila melanogaster Tip60 complex uses both its chromatin-remodelling and acetylation activities to catalyse the exchange of the histone variant H2Av (the fly homologue of human H2AX). By mimicking the phosphorylation of H2Av in a manner analogous to the DNA-damage-induced phosphorylation of mammalian H2AX, Kusch et al. found that histone exchange is enhanced by Tip60-mediated acetylation of phosphorylated H2Av. This could explain how phosphorylated H2AX is removed from the damage site.

Ageing

The AMP-activated protein kinase AAK-2 links energy levels and insulin-like signals to lifespan in C. elegans. Apfeld, J. et al. Genes Dev. 1 Dec 2004 (doi:10.1101/gad.1255404)

Limiting energy availability is thought to extend lifespan in some organisms. Apfeld and colleagues have now found that the cellular ratio of AMP:ATP, which is a measure of energy levels, increases with age in Caenorhabditis elegans. They also identified an enzyme, AMP-activated protein kinase α-subunit (AAK-2), that acts as a sensor of high levels of AMP and functions to extend lifespan.