The role of condensin in chromosome resolution

The condensin complex is a key determinant of mitotic chromosome architecture. In addition to its role in mitotic chromosome compaction, condensin is required for resolution of sister chromatid linkages during chromosome segregation in anaphase. How condensin resolves sister chromatids, and the nature of the chromosome bridges that are characteristic of cells harboring defective condensin, have remained topics of debate. Inactivation of topoisomerase II, the main enzyme that removes topological interlinks that persist between DNA replication products after their synthesis, leads to similar chromosome bridges. Here, we follow the catenation status of circular minichromosomes of three sizes during the S. cerevisiae cell cycle. Catenanes are produced in S-phase and, in part, they are readily resolved, aided by physical separation of sister chromatids during mitosis. Complete resolution, however, requires the condensin complex, a dependency that becomes more pronounced with increasing chromosome size. Condensin and topoisomerase II directly interact and, using purified proteins, we show that condensin stimulates DNA decatenation by topoisomerase II in vitro. Therefore, in parallel to promoting chromosome condensation, condensin facilitates topological resolution of sister chromatids to secure their successful segregation to daughter cells during cell division

Discriminación por grupo socioeconómico y meritocracia en el mercado laboral de Chile

Tesis para optar al grado de Magíster en Análisis EconómicoEste trabajo constituye un esfuerzo para determinar la existencia de discriminación salarial por origen socioeconómico y cuantificarla a través del tiempo. Empleando una base de datos con información de 577 egresados de Ingeniería Comercial de una de las mejores universidades de Chile, se logran constatar los siguientes hallazgos: (1) La brecha salarial no explicada -que en 1999 era desde un 29,8% hasta un 51,9% (dependiendo de la metodología empleada)- habría caído hasta un valor estimado entre un 12% y un 25,5%, dependiendo de la metodología empleada en su estimación. Sin embargo, esta caída aún no es estadísticamente significativa, por lo que el origen socioeconómico seguiría siendo un determinante salarial importante. (2) Se observan mayores niveles de meritocracia en el mercado laboral ya que, en 1999, el desempeño académico no lograba compensar ni siquiera la mitad de la brecha salarial asociada a origen socioeconómico. Mientras que, actualmente, sus efectos se igualan. Lo anterior indica que el mérito individual tiene un efecto tan fuerte sobre los salarios como el origen socioeconómico. Los resultados encontrados son robustos a distintas especificaciones y a la incorporación de variables que podrían medir el capital cultural transferido intergeneracionalmente. Por otra parte, la disminución en la importancia del origen socioeconómico parece estar relacionada con cambios sociales, aunque se requiere ahondar más en este último aspecto

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The segregation of eukaryotic chromosomes during mitosis requires their extensive folding into units of manageable size for the mitotic spindle. Here, we report on how phosphorylation at serine 10 of histone H3 (H3 S10) contributes to this process. Using a fluorescence-based assay to study local compaction of the chromatin fiber in living yeast cells, we show that chromosome condensation entails two temporally and mechanistically distinct processes. Initially, nucleosome-nucleosome interaction triggered by H3 S10 phosphorylation and deacetylation of histone H4 promote short-range compaction of chromatin during early anaphase. Independently, condensin mediates the axial contraction of chromosome arms, a process peaking later in anaphase. Whereas defects in chromatin compaction have no observable effect on axial contraction and condensin inactivation does not affect short-range chromatin compaction, inactivation of both pathways causes synergistic defects in chromosome segregation and cell viability. Furthermore, both pathways rely at least partially on the deacetylase Hst2, suggesting that this protein helps coordinating chromatin compaction and axial contraction to properly shape mitotic chromosomes. DOI: http://dx.doi.org/10.7554/eLife.10396.00

The SMC complex MukBEF recruits Topoisomerase IV to the origin of replication region in live Escherichia coli

The Escherichia coli Structural Maintenance of Chromosomes (SMC) complex, MukBEF, and topoisomerase IV (TopoIV) interact in vitro through a direct contact between the MukB dimerization hinge and the C-terminal domain of ParC, the catalytic subunit of TopoIV. The interaction stimulates catalysis by TopoIV in vitro. Using live cell quantitative imaging, we show that MukBEF directs TopoIV to ori, with fluorescent fusions of ParC and ParE both forming cellular foci that colocalize with those formed by MukBEF throughout the cell cycle and in cells unable to initiate DNA replication. Removal of MukBEF leads to loss of fluorescent ParC/ParE foci. In the absence of functional TopoIV, MukBEF forms multiple foci that are distributed uniformly throughout the nucleoid, whereas multiple catenated oris cluster at midcell. Once functional TopoIV is restored, the decatenated oris segregate to positions that are largely coincident with the MukBEF foci, thereby providing support for a mechanism by which MukBEF acts in chromosome segregation by positioning newly replicated and decatenated oris. Additional evidence for such a mechanism comes from the observation that in TopoIV+ cells, newly replicated oris segregate rapidly to the positions of MukBEF foci. Taken together, the data implicate MukBEF as a key component of the DNA segregation process, by acting in concert with TopoIV to promote decatenation and positioning of newly replicated oris.SCOPUS: ar.jinfo:eu-repo/semantics/publishe