Cell division

Role of the p53-homologue p73 in E2F1-induced apoptosis. Stiewe, T. & Pützer, B. M. Nature Genet. 26 , 464–469 (2000) [PubMed]

The transcription factor E2F1 can suppress tumorigenesis by prolonging the half-life of p53, through induction of p14ARF. Stiewe and Pützer now report a p53-independent mechanism of action for E2F: expression of the TP53 homologue TP73 is directly activated by E2F and can lead to the activation of pro-apoptotic genes in a p53-independent manner, providing an anti-tumorigenic 'safety catch' in the absence of functional p53.

Cell signalling

Quantitative imaging of lateral ErbB1 receptor signal propagation in the plasma membrane. Verveer, P. J. et al. Science 290 , 1567–1570 (2000) [PubMed]

Ligand-driven ErbB1 activation is believed to occur through the formation of stable receptor dimers in which receptors cross-phosphorylate each other. Verveer et al. use an ingenious imaging technique based on FRET and fluorescence-lifetime imaging microscopy to measure the activation of ErbB1 in living cells. They find that receptor dimers are in fact transient. After focal stimulation of ErbB1, receptor phosphorylation rapidly propagates over the entire cell surface in a ligand-independent manner, leading to the full activation of all receptors.

Protein-interaction mapping

A network of protein–protein interactions in yeast. Schwikowski, B., Uetz, P. & Fields, S. Nature Biotechnol. 18 , 1257–1261 (2000) [PubMed]

Proteins that associate with one another are likely to have similar functions. So if the function of one protein is known, those of its partners can be predicted. But first, a map of protein interactions must be built, and Fields and colleagues have done this in the yeast Saccharomyces cerevisiae. They analysed 2,709 published interactions and built up a network containing 2,358 interactions among over 1,500 proteins. Based on the functions of interacting partners, they then assigned possible functions to 364 previously uncharacterized proteins.

Nuclear transport

Vesicular stomatitis virus matrix protein inhibits host cell gene expression by targeting the nucleoporin Nup98. von Kobbe, C et al. Mol. Cell 6 , 1243–1252 (2000) [PubMed]

Vesicular stomatitis virus is an RNA virus that causes acute infections in many mammalian hosts. Of particular importance during infection is the viral matrix protein (M) which has pleiotropic effects, shutting off transcription and inhibiting nuclear export of certain RNA species. In this paper, von Kobbe et al. identify the cellular target of M as the nucleoporin Nup98, indicating that M specifically blocks nuclear export of RNAs, the inhibition of transcription being a secondary effect.