A Screen for Candidate Targets of Lysine Polyphosphorylation Uncovers a Conserved Network Implicated in Ribosome Biogenesis.

Polyphosphates (polyP) are chains of inorganic phosphates found in all cells. Previous work has implicated these chains in diverse functions, but the mechanism of action is unclear. A recent study reports that polyP can be non-enzymatically and covalently attached to lysine residues on yeast proteins Nsr1 and Top1.

Nicotinamide Suppresses the DNA Damage Sensitivity of Saccharomyces cerevisiae Independently of Sirtuin Deacetylases.

Nicotinamide is both a reaction product and an inhibitor of the conserved sirtuin family of deacetylases, which have been implicated in a broad range of cellular functions in eukaryotes from yeast to humans. Phenotypes observed following treatment with nicotinamide are most often assumed to stem from inhibition of one or more of these enzymes. Here, we used this small molecule to inhibit multiple sirtuins at once during treatment with DNA damaging agents in the Saccharomyces cerevisiae model system.

Yeast sterol regulatory element-binding protein (SREBP) cleavage requires Cdc48 and Dsc5, a ubiquitin regulatory X domain-containing subunit of the Golgi Dsc E3 ligase.

Schizosaccharomyces pombe Sre1 is a membrane-bound transcription factor that controls adaptation to hypoxia. Like its mammalian homolog, sterol regulatory element-binding protein (SREBP), Sre1 activation requires release from the membrane. However, in fission yeast, this release occurs through a strikingly different mechanism that requires the Golgi Dsc E3 ubiquitin ligase complex and the proteasome.

Yeast SREBP cleavage activation requires the Golgi Dsc E3 ligase complex.

Mammalian lipid homeostasis requires proteolytic activation of membrane-bound sterol regulatory element binding protein (SREBP) transcription factors through sequential action of the Golgi Site-1 and Site-2 proteases. Here we report that while SREBP function is conserved in fungi, fission yeast employs a different mechanism for SREBP cleavage. Using genetics and biochemistry, we identified four genes defective for SREBP cleavage, dsc1-4, encoding components of a transmembrane Golgi E3 ligase complex with structural homology to the Hrd1 E3 ligase complex involved in endoplasmic reticulum-associated degradation.

Analyzing mRNA localization to the endoplasmic reticulum via cell fractionation.

The partitioning of secretory and membrane protein-encoding mRNAs to the endoplasmic reticulum (ER), and their translation on ER-associated ribosomes, governs access to the secretory/exocytic pathways of the cell. As mRNAs encoding secretory and membrane proteins comprise approximately 30% of the transcriptome, the localization of mRNAs to the ER represents an extraordinarily prominent, ubiquitous, and yet poorly understood RNA localization phenomenon.The partitioning of mRNAs to the ER is generally thought to be achieved by the signal recognition particle (SRP) pathway.

Degradation of sterol regulatory element-binding protein precursor requires the endoplasmic reticulum-associated degradation components Ubc7 and Hrd1 in fission yeast.

Sre1, the fission yeast sterol regulatory element-binding protein (SREBP), is an endoplasmic reticulum (ER) membrane-bound transcription factor that is a principal regulator of hypoxic gene expression. Under low oxygen, Sre1 is cleaved from its inactive ER precursor form to generate an active nuclear transcription factor that up-regulates genes required for low oxygen growth. To maintain a constant supply of Sre1, Sre1 precursor synthesis must be regulated to replenish Sre1 precursor lost to proteolytic cleavage under low oxygen.