DNA repair

Involvement of human polynucleotide kinase in double-strand break repair by non-homologous end joining.Chappell, C. et al. EMBO J. 21, 2827–2832 (2002)

The efficient repair of double-strand breaks in DNA — by homologous recombination or by non-homologous end joining (NHEJ) — is vital to maintain genome stability. Chappell et al. now show that human polynucleotide kinase has a direct role in NHEJ. Acting specifically in the context of the NHEJ apparatus, this enzyme restores ligatable 5′-phosphate groups by catalysing the phosphorylation of 5′-OH termini.

Development

Sensory nerves determine the pattern of arterial differentiation and blood vessel branching in the skin.Mukouyama, Y. et al. Cell 109, 693–705 (2002)

In this report, Mukouyama and colleagues studied the effect of the nervous system on blood-vessel development in the embryonic mouse limb skin. They found that arteries, but not veins, specifically align with peripheral nerves, and that arteries fail to differentiate in mutant embryos that lack sensory nerves. In addition, they showed that arteries align with misrouted axons in mutant embryos containing disorganized nerves. Their results indicate that peripheral nerves provide a template that determines the organotypic branching pattern of blood vessels and arterial differentiation in the skin through the local secretion of vascular endothelial growth factor.

Transcription

Crystal structure of a bacterial RNA polymerase holoenzyme at 2.6 Å resolution.Vassylyev, D. G. et al. Nature 417, 712–719 (2002)

In bacteria, binding of the initiation factor σ to the RNA polymerase core enzyme produces the active holoenzyme that initiates transcription. Here, Vassylyev et al. describe the crystal structure of this holoenzyme, which provides insights into both the structural organization of transcription intermediate complexes and the mechanism of transcription initiation.

DNA segregation

Prokaryotic DNA segregation by an actin-like filament.Møller-Jensen, J. et al. EMBO J. 21, 3119–3127 (2002)

The mechanisms that underlie prokaryotic DNA segregation are not well defined. The Escherichia coli plasmid R1 par locus encodes a repressor (ParR), a cis-acting centromere-like region (parC) and an ATPase (ParM) — the function of which has been unclear. Here, the authors show that ParM forms actin-like filaments along the length of E. coli cells and this generates the force for plasmid segregation to opposite ends of the cell. Conversely, the ParR–parC complex functions as the point of nucleation for filament polymerization.