SummaryIn eukaryotic cells, there is evidence for functional coupling between transcription and processing of pre-mRNAs. To better understand this coupling, we performed a high-resolution kinetic analysis of transcription and splicing in budding yeast. This revealed that shortly after induction of transcription, RNA polymerase accumulates transiently around the 3′ end of the intron on two reporter genes. This apparent transcriptional pause coincides with splicing factor recruitment and with the first detection of spliced mRNA and is repeated periodically thereafter. Pausing requires productive splicing, as it is lost upon mutation of the intron and restored by suppressing the splicing defect. The carboxy-terminal domain of the paused polymerase large subunit is hyperphosphorylated on serine 5, and phosphorylation of serine 2 is first detected here. Phosphorylated polymerase also accumulates around the 3′ splice sites of constitutively expressed, endogenous yeast genes. We propose that transcriptional pausing is imposed by a checkpoint associated with cotranscriptional splicing.

P-bodies are cytoplasmic foci that are sites of mRNA degradation and translational repression. It is not known what causes the accumulation of RNA-degradation factors in Pbodies, although RNA is required. The yeast Lsm1-7p complex (comprising Lsm1p to Lsm7p) is recruited to P-bodies under certain stress conditions. It is required for efficient decapping and degradation of mRNAs, but not for the assembly of Pbodies. Here we show that the Lsm4p subunit and its asparagine-rich C-terminus are prone to aggregation, and that this tendency to aggregate promotes efficient accumulation of Lsm1-7p in P-bodies. The presence of glutamine-and/or asparagine-rich (Q/N-rich) regions in other P-body components suggests a more general role for aggregation-prone residues in P-body localization and assembly. This is supported by reduced P-body accumulation of Ccr4p, Pop2p and Dhh1p after deletion of these domains, and by the observed aggregation of the Q/Nrich region from Ccr4p. Supplementary material available online at

Zinc (Zn) is an essential micronutrient for plants and animals because of its structural and catalytic roles in many proteins. Zn deficiency affects ca. two billion people, mainly those living on plant-based diets that rely on crops from Zn deficient soils. Plants maintain adequate Zn levels through tightly regulated Zn homeostasis mechanisms, involving Zn uptake, distribution and storage, but it was not known how they sense Zn status. We use in vitro and in planta approaches to show that the Arabidopsis thaliana F-group bZIP transcription factors bZIP19 and bZIP23, which are the central regulators of the Zn deficiency response, act as Zn sensors by binding Zn 2+ ions to a Zn sensor motif (ZSM).Deletions or modifications of this ZSM disrupts Zn binding, leading to a constitutive transcriptional Zn deficiency response, which causes a significant increase in plant and seed Zn accumulation. Since the ZSM is highly conserved in F-bZIPs across land plants, the identification of the first plant Zn-sensor will promote new strategies to improve the Zn nutritional quality of plant-derived food and feed, and contribute to tackle the global Zn deficiency health problem.