Establishing a definitive cell cycle progression has been one of the fundamental aims of cellular biology. Its importance lies in gaining insight into the basic processes of life as well as the functions of mutant cell cycle pathways in promoting cancer by replication deficiencies and loss of checkpoint control. Currently used methods to control cell cycle and synchronize cells, function by halting cell cycle progression. Such harsh methods are detrimental to the cell and insufficient to provide an accurate reflection of the cell cycle. This study focused on replicating and confirming the efficiency of a technique developed by Helmstetter, called the “Baby Machine,” that can produce new born cells with little to no perturbations. Using this in conjunction with a short pulse RNA labelling technique, called Bru-seq, allowed the capture and RNA sequencing of synchronized cells and its nascent RNA. Here we show the first glimpse into the transcriptional profile of newly divided cells as well as novel rapid exon splicing and transcription read-through processes.

Eukaryotic promoters are inherently bidirectional and allow RNA Polymerase II to transcribe both coding and noncoding RNAs. Dynamic disassembly and reassembly is a prominent feature of nucleosomes around eukaryotic promoters. While H3K56 acetylation (H3K56Ac) enhances turnover events of these promoter-proximal nucleosomes, the chromatin remodeler INO80C ensures their proper positioning. In my dissertation, I explore how chromatin dynamics regulate transcriptional homeostasis. In the first part, I investigate the role of H3K56Ac on the nascent transcriptome throughout the eukaryotic cell cycle. I find that H3K56Ac is a global, positive regulator for coding and noncoding transcription by promoting both initiation and elongation/termination. On the contrary, I find that H3K56Ac represses promiscuous transcription following replication fork passage by ensuring efficient nucleosome assembly during S-phase. In addition, I show that there is a stepwise increase in transcription in the S-G2 transition, and this response to gene dosage imbalance does not require H3K56Ac. This study clearly shows that a single histone modification, H3K56Ac can exert both positive and negative effects on transcription at different cell cycle stages. In the second part, I investigate the role of the chromatin remodeler INO80C on the nascent transcription around replication origins. I show that INO80C, together with the transcription factor Mot1, prevents cryptic transcription around yeast replication origins, and the loss of these proteins lead to an increase in DNA double strand breaks. I hypothesize that recruitment of INO80C ensures proper positioning of nucleosomes around origins and the exclusion of RNA Pol II to prevent cryptic initiation. Together these findings indicate that H3K56Ac regulates transcription globally by enhancing nucleosome turnover, and it prevents cryptic transcription and reinforces transcriptional fidelity by promoting efficient nucleosome assembly in the S-phase. In addition, INO80C maintains genome stability by preventing cryptic transcription around the origins.