Astral MT shrinkage linked to Bud6p involves its direct interaction with Bim1p and the concerted action of two MT motors-Kip3p and dynein.

DNA breaks are complex DNA lesions that can be repaired by two alternative mechanisms: non-homologous end-joining and homologous recombination. The decision between them depends on the activation of the DNA resection machinery, which blocks non-homologous end-joining and stimulates recombination. On the other hand, post-translational modifications play a critical role in DNA repair. We have found that the SUMO E3 ligase CBX4 controls resection through the key factor CtIP. Indeed, CBX4 depletion impairs CtIP constitutive sumoylation and DNA end processing. Importantly, mutating lysine 896 in CtIP recapitulates the CBX4-depletion phenotype, blocks homologous recombination and increases genomic instability. Artificial fusion of CtIP and SUMO suppresses the effects of both the non-sumoylatable CtIP mutant and CBX4 depletion. Mechanistically, CtIP sumoylation is essential for its recruitment to damaged DNA. In summary, sumoylation of CtIP at lysine 896 defines a subpopulation of the protein that is involved in DNA resection and recombination.

DNA double strand breaks are the most cytotoxic lesions that can occur on the DNA. They can be repaired by different mechanisms and optimal survival requires a tight control between them. Here we uncover protein deneddylation as a major controller of repair pathway choice. Neddylation inhibition changes the normal repair profile toward an increase on homologous recombination. Indeed, RNF111/UBE2M-mediated neddylation acts as an inhibitor of BRCA1 and CtIP-mediated DNA end resection, a key process in repair pathway choice. By controlling the length of ssDNA produced during DNA resection, protein neddylation not only affects the choice between NHEJ and homologous recombination but also controls the balance between different recombination subpathways. Thus, protein neddylation status has a great impact in the way cells respond to DNA breaks.

The transcription factor CreA is the main regulator responsible for carbon repression in filamentous fungi. CreA is a wide domain regulator that binds to regulatory elements in the promoters of target genes to repress their transcription. Penicillin biosynthesis and the expression of penicillin biosynthetic genes are subject to carbon repression. However, evidence of the participation of CreA in this regulation is still lacking, and previous studies on the promoter of the pcbC gene of Aspergillus nidulans indicated the lack of involvement of CreA in its regulation. Here we present clear evidence of the participation of CreA in carbon repression of penicillin biosynthesis and expression of the pcbAB gene, encoding the first enzyme of the pathway, in Penicillium chrysogenum. Mutations in cis of some of the putative CreA binding sites present in the pcbAB gene promoter fused to a reporter gene caused an important increase in the measured enzyme activity in glucose-containing medium, whereas activity in the medium with lactose was not affected. An RNAi strategy was used to attenuate the expression of the creA gene. Transformants expressing a small interfering RNA for creA showed higher penicillin production, and this increase was more evident when glucose was used as carbon source. These results confirm that CreA plays an important role in the regulation of penicillin biosynthesis in P. chrysogenum and opens the possibility of its utilization to improve the industrial production of this antibiotic.

We show that Kar9p polarity is instructed by a feedback loop that requires astral microtubules, actin cables, and Myo2p-based transport to enforce Kar9p loading to the bud-ward pole. This novel mechanism also provides the basis for a model unifying Kar9p polarity and the stereotyped pattern of spindle pole inheritance known to occur in yeast.

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There are multiple processes that occur at certain points during the cell cycle and that affect later steps. Impairment of such processes could cause delays or even completely abolish cell cycle progression. Therefore, it is extremely helpful in order to determine the potential consequences that interfering on a cellular process imposes on cell cycle progression to be able to precisely characterize the cell cycle stage by using molecular markers. Here, we describe the analysis of the protein levels of known mitotic regulators as molecular markers to monitor the progression of cells through the cell cycle by western blot in synchronized yeast cell cultures.