Studies on the mechanism of Ndt80 repressing DNA replication

Ndt80 is a meiosis-specific transcription activator in the budding yeast Saccharomyces cerevisiae. ndt80 null mutants arrest at the pachytene stage and fails to complete meiosis. Interestingly, our laboratory found that ectopic expression of NDT80 in vegetative cells causes cell cycle arrest at G1 phase, and we proposed that Ndt80 may be involved in repressing another round of DNA replication between meiosis I and meiosis II. In recent research, our results showed that Ndt80 had the ability to partially repress pre-meiotic DNA replication when expressed at a stage when origin of replication is at a post-RC state. The DNA repression effect grew stronger when continuously expressing Ndt80 throughout pre-meiotic incubation. Despite these discoveries, it is still important to analyze the role of Ndt80 repressing DNA replication when it is normally expressed, meiosis I and meiosis II. Therefore, we screened for a separation-of-function mutant that can promote cells to complete meiosis but cannot cause cell cycle arrest. The repression of DNA replication by Ndt80 could be resulted from a direct binding of Ndt80 to DNA sequences, or indirectly from the effect of cell cycle related genes regulated by Ndt80. In this study, we discussed the possible mechanisms of Ndt80 repressing DNA replication. First, we expressed Ndt80 in a ime2 null strain to test if Ndt80-induced cell cycle arrest rely on IME2. Results showed that IME2 is not responsible for causing Ndt80-induced cell cycle arrest. Second, we tested the possibility of Ndt80 binding to Sum1 binding sites near ARSs to repress DNA replication. We expressed Ndt80 in a sum1 null strain to see if removing Sum1 competition would affect cell cycle arrest effects, but no significant difference was observed. Further analyses are required to explore the mechanisms of Ndt80 repressing DNA replication.