Correspondingly, microscopic analysis revealed abnormal morphological changes in these mutants. WT cells were rod shaped and contained a single nucleus, or double nuclei separated by a sharp septum. In contrast, mutant cells exhibited elongated cell length, multiple nuclei, thick septum or multiple septa, resembling typical defects in cytokinesis. As expected, all 4 deletions dis played strong sensitivity to TBZ, a microtubule depoly merizing agent. Microarray and real time PCR analysis showed that the expressions of several cytokinesis related genes were up regulated in the mutants, including those of ace2, agn1 and eng1. Ace2 is a transcription factor that controls the expression of genes required for cell separation, while eng1 and agn1 are both targets of Ace2.

Eng1, a B glucanase, degrades the primary division septum between the new ends of daughter cells. Agn1, an glucanase, hydrolyses the old cell wall sur rounding the septum and leads to full separation of Inhibitors,Modulators,Libraries daugh ter cells. The data suggest that deletion of sgf73, meu29, sec65 or pab1 delays proper progression of cyto kinesis, while a ruptured cell wall constitutively generates a signal to activate the Ace2 pathway and up regulate target genes. On the other hand, diploidization could also result from DNA re replication during one cell cycle. Consis tent with this idea, expression levels of cdc18 and cdt1 were up regulated in all 4 mutants. Presence of Cdc18 and Cdt1 at pre RCs is Inhibitors,Modulators,Libraries important for efficient DNA replication initiation, and inactivation of these pro teins after initiation is crucial to ensure only one round of DNA replication in each cell cycle.

Overexpression of cdc18 and cdt1 in fission yeast causes repli cation origins to re fire, and drive re replication Batimastat of DNA sequences genome wide. Therefore, up regulation of cdc18 and cdt1 in sgf73, meu29, sec65 and pab1 might lead to DNA re replication, and that contributes to the observed diploidization. Meanwhile, disturbed replication initiation probably compromises DDR during early S phase. Correspon dingly, all the members in W4C and S4C groups showed strong sensitivities to HU. Discussion In this study, six reagents were applied in the screen and they can cause different kinds of DNA damage. The screen revealed six genes whose deletions displayed strong sensitivities to five reagents, Inhibitors,Modulators,Libraries including rad1, rhp55, ulp2, pst2, mlo3 and trk1.

Broad sensitivities to different DNA damage reagents suggest that these genes function in the universal pathway of DDR, for example, in the conserved ATM ATR pathway. As expected, rad1 plays a role in the ATR pathway, and rhp55 in the ATM pathway. ulp2, encoding Inhibitors,Modulators,Libraries a SUMO protease, is required for cell division after termination of the DNA damage checkpoint. The high sensitivity of ulp2 to a broad range of DNA damage reagents emphasizes the importance of silencing of the DNA damage checkpoint and restart of the cell cycle.