Xuyang Li:
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The regulation of the cell cycle is important to all living organisms and is frequently exploited by viruses to enhance their own replication. Nevertheless, our understanding of cell cycle control in archaea remains significantly limited. We have two main objectives for this project. In Chapter 1, we discover and characterize aCcr-1, a conserved, essential protein in Sulfolobales that controls the programs of the cell cycle. It was found everywhere in Thermoproteota within the Sulfolobales order and their viruses. The overexpression of multiple aCcr1 members, such as gp21 from the rudivirus SIRV2 and its corresponding host protein SiL_0190 from S. islandicus LAL14/1, leads to the disruption of cell division. This is evidenced by a slowdown in growth, an increase in cell size, and a rise in cellular DNA content. Moreover, both gp21 and SiL_0190 have the ability to bind to the AGTATTA motif, which is conserved in the promoters of multiple genes involved in cell division, DNA replication, and cellular metabolism, thus either repressing or activating their transcription.
Our research suggests that aCcr1 suppresses cell division and promotes transition to the S-phase in Sulfolobales. a function exploited by viruses to facilitate viral propagation. However, the exact regulatory strategy remains unclear. Next, we want to further investigate the mechanism of the cell cycle regulation in Sulfolobus and discover the crucial genes that may involve in complex cell cycle control, this part of the project was illustrates in Chapter 2. In Chapter 2, we focus on the regulation of gene expression during the cell cycle in the model species S. islandicus LAL14/1. With the successful cell cycle synchronization of S. islandicus LAL14/1, the integration analysis through transcriptomic and proteomic data reveals the following key observations: Firstly, in total the 920 DEGs and 275 DEPs were identified across the cell cycle of LAL14/1, the significant global changes occur at the transcriptomic level throughout the cell cycle, while such changes are less pronounced at the proteomic level. Next, based on the COG dataset, the expression patterns of the differentially expressed genes related to cell cycle regulation exhibit periodically pattern during three VI essential transition phases: D to G1 transition phase, G1 phase and early S phase.
Additionally, apart from aCcr-1, three transcriptional regulators and one acetyltransferase with crucial roles during the cell cycle were identified. Remarkably, one of the transcriptional regulators (SIL_RS07870, named aCcr-2), a homolog of aCcr-1, belonging to another cellular branch, shows significant expression at both RNA and protein levels. This suggests the possibility of aCcr-2 performing a novel and distinct function in cell cycle regulation. The chapter 2 also includes a comparative analysis of the expression patterns of cell-cycle-regulated genes in S. acidocaldarius and S. islandicus LAL14/1, several essential cell-cycle-associated genes with different expression pattern were identified, this may provide insights into evolutionary relationships among the three domains of life.
Our work significantly contributes to a deeper understanding of archaeal cell cycle regulatory mechanisms, unveiling the fundamental rules governing the cell cycle and identifying key cell-cycle-regulation-associated genes and their regulatory strategies throughout the archaeal cell cycle