Proper spatial and temporal regulation of the cell cycle is crucial to the survival and proliferation of all organisms. To ensure stable, orderly cell cycle progression, cells employ complex genetic circuits. The architecture, operation, and design principles of such circuits remain only poorly understood. The bacterium Caulobacter crescentus provides an experimentally tractable system for studying genetic circuits and for elucidating fundamental molecular mechanisms of cell cycle regulation. In C. crescentus the cell cycle is driven by the periodic rise and fall in activity of a master regulator, CtrA. Active CtrA directly regulates the expression of nearly 100 genes, many of which coordinate cell division. CtrA also directly binds to and silences the origin of replication. Cell cycle progression therefore requires oscillations in CtrA activity - it must be cleared from the cell to permit DNA replication, but must accumulate to drive cell division. The outline of a genetic circuit controlling CtrA is in place, but does not yet fully account for the dynamics of CtrA activity. Additional components and levels of regulation must exist. The goal of this project is to define the complete molecular circuitry that controls CtrA activity and hence ensures orderly progression through the cell cycle. To this end, we will: (i) map the pathways that regulate phosphorylation and dephosphorylation of CtrA, (ii) elucidate how cells control the sub-cellular localization and activity of CckA, the primary phosphodonor for CtrA (iii) examine how multiple transcriptional feedback loops collaborate to precisely control the induction dynamics of CtrA, and (iv) identify and characterize additional factors that regulate CtrA activity. These studies will help to unveil how cells use multiple modes of regulation to successfully navigate their cell cycle. In addition, this work will help to reveal the general design and operating principles of genetic circuits, which underlie regulatory processes throughout biology. Finally, a better understanding of how bacteria regulate the cell cycle may help guide the development of new antibiotics, a problem of increasing public-health relevance.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Prokaryotic Cell and Molecular Biology Study Section (PCMB)
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Hamlet, Michelle R
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Massachusetts Institute of Technology
Schools of Arts and Sciences
United States
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Le, Tung Bk; Laub, Michael T (2016) Transcription rate and transcript length drive formation of chromosomal interaction domain boundaries. EMBO J 35:1582-95
Lubin, Emma A; Henry, Jonathan T; Fiebig, Aretha et al. (2016) Identification of the PhoB Regulon and Role of PhoU in the Phosphate Starvation Response of Caulobacter crescentus. J Bacteriol 198:187-200
Wang, Xindan; Le, Tung B K; Lajoie, Bryan R et al. (2015) Condensin promotes the juxtaposition of DNA flanking its loading site in Bacillus subtilis. Genes Dev 29:1661-75
Badrinarayanan, Anjana; Le, Tung B K; Laub, Michael T (2015) Bacterial chromosome organization and segregation. Annu Rev Cell Dev Biol 31:171-99
Aakre, Christopher D; Herrou, Julien; Phung, Tuyen N et al. (2015) Evolving new protein-protein interaction specificity through promiscuous intermediates. Cell 163:594-606
Haakonsen, Diane L; Yuan, Andy H; Laub, Michael T (2015) The bacterial cell cycle regulator GcrA is a σ70 cofactor that drives gene expression from a subset of methylated promoters. Genes Dev 29:2272-86
Badrinarayanan, Anjana; Le, Tung B K; Laub, Michael T (2015) Rapid pairing and resegregation of distant homologous loci enables double-strand break repair in bacteria. J Cell Biol 210:385-400
Salazar, Michael E; Laub, Michael T (2015) Temporal and evolutionary dynamics of two-component signaling pathways. Curr Opin Microbiol 24:7-14
Leslie, David J; Heinen, Christian; Schramm, Frederic D et al. (2015) Nutritional Control of DNA Replication Initiation through the Proteolysis and Regulated Translation of DnaA. PLoS Genet 11:e1005342
Le, Tung Bk; Laub, Michael T (2014) New approaches to understanding the spatial organization of bacterial genomes. Curr Opin Microbiol 22:15-21

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