A novel RHH family transcription factor aCcr1 and its viral homologs dictate cell cycle progression in archaea [ChIP-seq]

Cell cycle regulation is of paramount importance for all forms of life. Here we report that a conserved and essential cell cycle-specific transcription factor (designated as aCcr1) and its viral homologs control cell division in Sulfolobales. We show that the transcription level of accr1 reaches peak during active cell division (D-phase) subsequent to the expression of CdvA, an archaea-specific cell division protein. Cells over-expressing the 58-aa-long RHH (ribbon-helix-helix) family cellular transcription factor as well as the homologs encoded by large spindle-shaped viruses Acidianus two-tailed virus (ATV) and Sulfolobus monocaudavirus 3 (SMV3) display significant growth retardation and cell division failure, manifested as enlarged cells with multiple chromosomes. aCcr1 over-expression results in downregulation of 17 genes (>4-folds) including cdvA. A conserved motif, aCcr1-box, located between the TATA-binding box and the translation initiation site in the promoters of 13 out of the 17 highly repressed genes, is critical for aCcr1 binding. The aCcr1-box is present in the promoters of cdvA genes across Sulfolobales, suggesting that aCcr1-mediated cdvA repression is an evolutionarily conserved mechanism by which archaeal cells dictate cytokinesis progression, whereas their viruses take advantage of this mechanism to manipulate the host cell cycle. Overall design: Chromatin immunoprecipitation (ChIP-Seq) was performed according to Takemata et al.(39) with slight modifications. Briefly, the cells were collected 3 hours after synchronization, cross-linked by adding 1% formaldehyde for 15 minutes, and quenched with a final concentration of 125 mM glycine. The cells were pelleted by centrifugation at 5,000 g for 10 minutes and washed with PBS. The cells were then resuspended in TBS-TT buffer (20 mM Tris, 150 mM NaCl, 0.1% Tween-20, 0.1% Triton X-100, pH 7.5) and fragmented by sonication until the DNA fragments were of 200-500 bp. After centrifugation (10,000 g for 15 minutes), a 100 µl aliquot of the DNA-containing supernatant was kept apart to be uses as an input control and the remaining sample was divided into two aliquots. One aliquot was incubated with anti-aCcr1 antibody-coated protein A beads (Cytiva) and the other was incubated with pre-immune serum-coated protein A beads, which served as a nonspecific binding control (Mock control). After incubation at 60 °C for 10 hrs, the samples were collected and the captured DNA was purified by using the DNA Cycle-Pure Kit (Omega) according to the manufacturer's instruction. The input samples were treated as above without the addition of antiserum and beads. The purified DNA was used for ChIP-Seq library preparation. The library was constructed by Novogene Corporation (Beijing, China). Subsequently, pair-end sequencing of sample was performed on Illumina platform (Illumina, CA, USA). Library quality was assessed on the Agilent Bioanalyzer 2100 system