Unloading of Condensin from rDNA is compromised in lte1 mutants in S. cerevisiae.
Elisa Varela (1), Didier Leroy (2), Thierry Laroche (1), Susan M. Gasser (1)
(1) Friedrich Miescher Institute, Novartis Research Foundation, Maulbeerstrasse 66, Basel, 4058, Switzerland; (2) Serono International SA, 15bis Chemin Des Mines, Geneva, Switzerland
Barren, Brn1p in S. cerevisiae, was identified in a screen for events that affected peripheral nervous system in Drosophila. It is essential for viability in yeast and affects chromosome condensation and segregation in S. cerevisiae. The present study shows that in S. cerevisiae, Brn1p expression is constant throughout the cell cycle, immunoprecipitates with another subunit of the condensing complex (Smc2) , and is modified during mitosis. We have also found interaction with a new partner, Lte1, the guanine nucleotide exchange factor for Tem1p. During late anaphase, Lte1p activates the mitotic exit network. Localization of Brn1p is nuclear, showing a heterogeneous distribution over the chromatin during interphase. In late mitosis, Brn1p staining becomes structured forming a spiral that extends the length of the dividing mitotic nucleus, colocalizing with the rDNA. Double staining for Brn1p with the histone H3-P-Ser10 or topoisomerase II shows that their localization is mutually exclusive. We have tested Brn1p phenotype in the lte1 mutant, which is cold sensitive and have found that at low temperature Brn1p remains structured during completion of mitosis and during G1, suggesting a defect in unloading of Brn1p from the rDNA. We have also analysed the net1-1 mutant, which have been shown to bypass mitotic exit defect of cdc15 mutant. Here Brn1p staining is highly structured throughout the cell cycle.