The RNA-binding protein Puf5 contributes to buffering of mRNA upon chromatin-mediated changes in nascent transcription.

Gene expression involves regulation of chromatin structure and transcription, as well as processing of the transcribed mRNA. While there are feedback mechanisms, it is not clear whether these include crosstalk between chromatin architecture and mRNA decay. To address this, we performed a genome-wide genetic screen using a Saccharomyces cerevisiae strain harbouring the H3K56A mutation, which is known to perturb chromatin structure and nascent transcription. We identified Puf5 (also known as Mpt5) as essential in an H3K56A background. Depletion of Puf5 in this background leads to downregulation of Puf5 targets. We suggest that Puf5 plays a role in post-transcriptional buffering of mRNAs, and support this by transcriptional shutoff experiments in which Puf5 mRNA targets are degraded slower in H3K56A cells compared to wild-type cells. Finally, we show that post-transcriptional buffering of Puf5 targets is widespread and does not occur only in an H3K56A mutant, but also in an H3K4R background, which leads to a global increase in nascent transcription. Our data suggest that Puf5 determines the fate of its mRNA targets in a context-dependent manner acting as an mRNA surveillance hub balancing deregulated nascent transcription to maintain physiological mRNA levels.

The mRNA decapping complex is buffered by nuclear localization.

mRNA decay is a key step in regulating the cellular proteome. Processing bodies (P-bodies) are thought to be sites of mRNA decay and/or storage. P-body units assemble into P-body granules under stress conditions. How this assembly is regulated, however, remains poorly understood. Here, we show, in the yeast Saccharomyces cerevisiae, that the translational repressor Scd6 and the decapping stimulator Edc3 act partially redundantly in P-body assembly by sequestering the Dcp1-Dcp2 (denoted Dcp1/2) decapping complex in the cytoplasm and preventing it from becoming imported into the nucleus by the karyopherin ß protein Kap95. One of two nuclear localization signals in Dcp2 overlaps with the RNA-binding site, suggesting an additional mechanism to regulate Dcp1/2 localization. Nuclear Dcp1/2 does not drive mRNA decay and might be stored there as a readily releasable pool, indicating a dynamic equilibrium between cytoplasmic and nuclear Dcp1/2. Cytoplasmic Dcp1/2 is linked to Dhh1 via Edc3. Functional P-bodies are present at the endoplasmic reticulum where Dcp2 potentially acts to increase the local concentration of Dhh1 through interaction with Edc3 to drive phase separation and hence P-body formation.

Dual Role of an mps-2/KCNE-Dependent Pathway in Long-Term Memory and Age-Dependent Memory Decline.

Activity-dependent persistent changes in neuronal intrinsic excitability and synaptic strength are underlying learning and memory. Voltage-gated potassium (Kv) channels are potential regulators of memory and may be linked to age-dependent neuronal disfunction. MinK-related peptides (MiRPs) are conserved transmembrane proteins modulating Kv channels; however, their possible role in the regulation of memory and age-dependent memory decline are unknown. Here, we show that, in C. elegans, mps-2 is the sole member of the MiRP family that controls exclusively long-term associative memory (LTAM) in AVA neuron. In addition, we demonstrate that mps-2 also plays a critical role in age-dependent memory decline. In young adult worms, mps-2 is transcriptionally upregulated by CRH-1/cyclic AMP (cAMP)-response-binding protein (CREB) during LTAM, although the mps-2 baseline expression is CREB independent and instead, during aging, relies on nhr-66, which acts as an age-dependent repressor. Deletion of nhr-66 or its binding element in the mps-2 promoter prevents age-dependent transcriptional repression of mps-2 and memory decline. Finally, MPS-2 acts through the modulation of the Kv2.1/KVS-3 and Kv2.2/KVS-4 heteromeric potassium channels. Altogether, we describe a conserved MPS-2/KVS-3/KVS-4 pathway essential for LTAM and also for a programmed control of physiological age-dependent memory decline.

Dialdehydes lead to exceptionally fast bioconjugations at neutral pH by virtue of a cyclic intermediate.

One of the open challenges in chemical biology is to identify reactions that proceed with large rate constants at neutral pH values. As shown here, dialdehydes react with O-alkylhydroxylamines at rates of 500 M(-1) s(-1) at neutral pH values in the absence of catalysts. The key to these conjugations is an unusually stable cyclic intermediate, which ultimately undergoes dehydration to yield an oxime. The scope and limitations of the method are outlined, as well as its application in bioconjugation and a mechanistic interpretation that will facilitate further developments of reactions with alkylhydroxylamines at low substrate concentrations.