Cell signalling

The ankyrin repeat protein Diversin recruits Casein kinase IE to the β-catenin degradation complex and acts in both canonical Wnt and Wnt/JNK signaling.Schwarz-Romond, T. et al. Genes Dev. 16, 2073–2084 (2002)

This study describes a new vertebrate protein — Diversin — that is an essential component of the Wnt signalling pathway. Diversin acts as a molecular switch. It inhibits signals mediated by the canonical Wnt/β-catenin pathway, which controls formation of the embryonic axis, and, at the same time, activates the Wnt/JNK signalling pathway, which establishes gastrulation movements in vertebrates.

Gene expression

A recombinant RNA polymerase II-like enzyme capable of promoter-specific transcription.Werner, F. & Weinzierl, R. O. J. Mol. Cell 10, 635–646 (2002)

So far, attempts to reconstitute active eukaryotic RNA polymerase (RNAP)-II from its individual subunits have failed. However, Werner and Weinzierl now report the successful in vitro assembly of the RNAPII-like, archaeal RNAP from purified recombinant subunits. The recombinant enzyme is fully active and, together with basal transcription factors TBP and TFB, is capable of promoter-specific transcription. This in vitro assembly approach also provided the authors with a unique opportunity to use mutagenesis studies to assess the functional contribution of individual subunits.

Cell signalling

A family of Rhomboid intramembrane proteases activates all Drosophila membrane-tethered EGF ligands.Urban, S. et al. EMBO J. 21, 4277–4286 (2002)

Keren, a new ligand of the Drosophila epidermal growth factor receptor, undergoes two modes of cleavage.Reich, A. & Shilo, B. Z. EMBO J. 21, 4287–4296 (2002)

In the first of two papers that highlight the Drosophila EGF receptor (DER) pathway, Urban et al. investigated the processing of the DER ligands Spitz, Gurken and Keren. Rhomboid-1 is involved in the activation of Spitz by proteolytic cleavage, and analysis of four members of the Rhomboid family showed that Rhomboids 1–4 can proteolytically activate all three DER ligands. This common cleavage mechanism is distinct from that used to activate mammalian EGF-like ligands. In the second paper, Reich and Shilo describe the previously uncharacterized DER ligand Keren. Although Keren is processed as described above, proteolytic activation can also occur in a Rhomboid-independent manner, which highlights the complex regulation of this signalling pathway.