Transcription

Dynamic association of capping enzymes with transcribing RNA polymerase II. Schroeder, C. et al. Genes Dev. 14, 2435?2440 (2000) [ PubMed]

Different phosphorylated forms of RNA polymerase II and associated mRNA processing factors during transcription. Komarnitsky, P., Cho, E.-J. & Buratowski, S. Genes Dev. 14, 2452?2460 (2000) [ PubMed]

RNA polymerase II is a molecular platform to which many messenger RNA-processing factors bind during transcription. Are such factors associated simultaneously with RNA pol II, or do they interact in a transient and sequential manner? Using mRNA-capping enzymes, both papers indicate that RNA-processing enzymes associate dynamically with differently modified forms of the polymerase at different stages of the transcriptional cycle.

Cell polarity

Plasma membrane compartmentalization in yeast by messenger RNA transport and a septin diffusion barrier. Takizawa, P. A. et al. Science 290, 341?344 (2000) [ PubMed]

Saccharomyces cerevisiae restricts the cellular distribution of the transcription factor Ash1p by transporting its messenger RNA into the forming bud. Takizawa et al. now present a list of other mRNAs that also localize to the bud, and the transport mechanism for at least one of them ? which encodes a transmembrane protein ? is the same as for ASH1 mRNA. The protein is then retained in the bud by a diffusion barrier involving septins that is functionally similar to tight junctions in epithelial cells.

Cell signalling

RasGRP is essential for mouse thymocyte differentiation and TCR signalling. Dower, N. A. et al. Nature Immunol. 1, 317?321 (2000) [Contents page]

Control of pre-T cell proliferation and differentiation by the GTPase Rac-1. Gomez, M. et al. Nature Immunol. 1, 317?321 (2000) [Contents page]

These papers describe the actions of two small GTPases, Ras and Rac, in T-cell responses. The first sheds light on how RasGRP, a Ras activator that's directly sensitive to diacylglycerol, mediates responses that had previously been assumed to be a result of the archetypal diacylglycerol-sensitive enzyme ? protein kinase C. The second uses Rac mutants that can control actin dynamics, but not other downstream targets of Rac such as mitogen-activated protein kinases, to show that changes in actin dynamics are sufficient to drive some stages of T-cell differentiation.