Mitochondrial dysfunction can lead to diverse cellular and organismal responses. We used DNA microarrays to characterize the transcriptional responses to different mitochondrial perturbations in Saccharomyces cerevisiae. We examined respiratory-deficient petite cells and respiratory-competent wild-type cells treated with the inhibitors of oxidative phosphorylation antimycin, carbonyl cyanide m-chlorophenylhydrazone, or oligomycin. We show that respiratory deficiency, but not inhibition of mitochondrial ATP synthesis per se, induces a suite of genes associated with both peroxisomal activities and metabolite-restoration (anaplerotic) pathways that would mitigate the loss of a complete tricarboxylic acid cycle. The array data suggested, and direct microscopic observation of cells expressing a derivative of green fluorescent protein with a peroxisomal matrix-targeting signal confirmed, that respiratory deficiency dramatically induces peroxisome biogenesis. Transcript profiling of cells harboring null alleles of RTG1, RTG2, or RTG3, genes known to control signaling from mitochondria to the nucleus, suggests that there are multiple pathways of cross-talk between these organelles in yeast.

Accurate chromosome segregation during cell division requires not only the establishment, but also the precise, regulated release of chromosome cohesion. Chromosome dynamics during meiosis are more complicated, because homologues separate at anaphase I whereas sister chromatids remain attached until anaphase II. How the selective release of chromosome cohesion is regulated during meiosis remains unclear. We show that the aurora-B kinase AIR-2 regulates the selective release of chromosome cohesion during Caenorhabditis elegans meiosis. AIR-2 localizes to subchromosomal regions corresponding to last points of contact between homologues in metaphase I and between sister chromatids in metaphase II. Depletion of AIR-2 by RNA interference (RNAi) prevents chromosome separation at both anaphases, with concomitant prevention of meiotic cohesin REC-8 release from meiotic chromosomes. We show that AIR-2 phosphorylates REC-8 at a major amino acid in vitro. Interestingly, depletion of two PP1 phosphatases, CeGLC-7α and CeGLC-7β, abolishes the restricted localization pattern of AIR-2. In Ceglc-7α/β(RNAi) embryos, AIR-2 is detected on the entire bivalent. Concurrently, chromosomal REC-8 is dramatically reduced and sister chromatids are separated precociously at anaphase I in Ceglc-7α/β(RNAi) embryos. We propose that AIR-2 promotes the release of chromosome cohesion via phosphorylation of REC-8 at specific chromosomal locations and that CeGLC-7α/β, directly or indirectly, antagonize AIR-2 activity.

Abstract. In yeast, actin forms patches associated with the plasma membrane. Patch distribution correlates with polarized growth during the cell cycle and in response to external stimuli. Using green fluorescent protein fused to capping protein to image actin patches in living cells, we find that patches move rapidly and over long distances. Even patches in clusters, such as at the incipient bud site, show movement. Patches move independently of one another and generally over small distances in a local area, but they can also move larger distances, including through the mother-bud neck. Changes in patch polarization occur quickly through the cell cycle. These observations provide important new parameters for a molecular analysis of the regulation and function of actin.I r~ yeast, actin functions in polarized secretion and growth (6, 37). Actin filaments in yeast are found in cortical patches associated with invaginations of the plasma membrane and in cables running through the cytoplasm (26). The polarization of patches and the orientation of cables correlates with polarized cell growth (1). The distribution of both patches and cables changes dramatically over time during the cell cycle and in response to external stimuli (10). Cell cycle regulators control the redistribution processes (20), and several actin-binding proteins are necessary for patch polarization and cable formation (6, 37).Actin is essential for viability (31). Mutants lacking patches have never been observed, but mutants without cables are viable. Also, mutations in genes encoding other protein components of patches are lethal (2, 25). Therefore, patches may be the location of the essential function of actin. Temperature shift experiments indicate that actin is important for secretion (27) and endocytosis (19). Together, these observations suggest that the location of patch polarization specifies the location of polarized growth and cell wall remodelling.Therefore, we wish to understand how the location of cortical actin patches in a living yeast cell is controlled. In particular, we want to determine whether patches change their distribution by moving about or by disassembly at one place with re-assembly elsewhere. Also, we want to understand how rapidly the patches change between polarized and depolarized states. These pieces of information An analysis of actin patch dynamics is now possible in yeast with the advent of green fluorescent protein (GFP) t technology (33). We constructed a GFP derivative of the 13 subunit of capping protein (Cap2p) because capping protein is found only at cortical actin patches (3). GFP-Cap2p localized to patches and was able to function like Cap2p, rescuing a null mutant.We found that the distribution of patches changed on a time scale of seconds, much faster than landmark events through the cell cycle. Patches moved, at rapid rates and over long distances, even through the mother/bud neck. Even polarized patches, found in clusters at incipient bud sites, in the bud and at cell division sites, showed movement. A...

Glucose represses the transcription of many genes in bakers yeast (Saccharomyces cerevisiae). Mig1 is a Cys2-His2 zinc finger protein that mediates glucose repression of several genes by binding to their promoters and recruiting the general repression complex Ssn6-Tup1. We have found that the subcellular localization of Mig1 is regulated by glucose. Mig1 is imported into the nucleus within minutes after the addition of glucose and is just as rapidly transported back to the cytoplasm when glucose is removed. This regulated nuclear localization requires components of the glucose repression signal transduction pathway. An internal region of the protein separate from the DNA binding and repression domains is necessary and sufficient for glucose-regulated nuclear import and export. Changes in the phosphorylation status of Mig1 are coincident with the changes in its localization, suggesting a possible regulatory role for phosphorylation. Our results suggest that a glucose-regulated nuclear import and/or export mechanism controls the activity of Mig1.

The CCCH finger protein PIE-1 is a regulator of germ cell fate that segregates with the germ lineage in early embryos. At each asymmetric division, PIE-1 is inherited preferentially by the germline daughter and is excluded from the somatic daughter. We show that this asymmetry is regulated at the protein level by two complementary mechanisms. The first acts before cell division to enrich PIE-1 in the cytoplasm destined for the germline daughter. The second acts after cell division to eliminate any PIE-1 left in the somatic daughter. The latter mechanism depends on PIE-1's first CCCH finger (ZF1), which targets PIE-1 for degradation in somatic blastomeres. ZF1s in two other germline proteins, POS-1 and MEX-1, are also degraded in somatic blastomeres, suggesting that localized degradation also acts on these proteins to exclude them from somatic lineages.