Associate Professor;
Microbial physiology/Genetics
Cell cycle and developmental control of chromosomal replication
Accepting graduate students
Lyman Duff Medical Building
3775 University St., Room 506
Montreal, QC H3A 2B4
Tel: (514) 398-3917
Fax: (514) 398-7052
gregory [dot] marczynski [at] mcgill [dot] ca (Email)
Research Orientations
We wish to understand how chromosome replication is coordinated with cellular growth and development so that replication occurs during the appropriate period of the cell cycle, and in the appropriate cell-type during cellular differentiation. The bacterium Caulobacter crescentus exemplifies this fundamental control problem, because its cellular differentiation is an obligate part of its cell division cycle, and chromosome replication does not initiate until the "swarmer" cell-type differentiates into the "stalked" cell-type. In both C. crescentus and E. coli, chromosome replication begins at a unique place, the origin of replication. However, despite the detailed knowledge of the biochemical interactions that take place at the E. coli origin, very little is actually known about the molecular mechanisms that couple replication to the cell cycle in this or any other bacterium. Presumably, special proteins monitor growth and relay the appropriate signals to the replication proteins at the origin of replication.
In C. crescentus, where the cell cycle is more amenable to analysis, we propose that a key signaling protein (CtrA) couples replication with the cell cycle. This hypothesis is based on the CtrA protein's homology with a class of phosphorelay proteins (the OmprR response regulators) whose biochemical activities are altered by special phosphokinase proteins, and our recent results demonstrating that CtrA protein has five binding sites inside the C. crescentus origin of replication (Cori). Interestingly, Cori CtrA binding sites overlap an essential RNA polymerase promoter and an essential DnaA protein binding site, implying that CtrA may directly interact with these proteins that are thought to be the earliest acting proteins at the E. coli origin of replication. Despite the ubiquity of phosphorelay proteins, and the universal requirement for replication control, CtrA is the first candidate response regulator with a direct role in replication control.
We are currently testing the hypothesis that CtrA is a major regulator of chromosome replication by employing several molecular genetic and biochemical approaches, and we are particularly interested in understanding how CtrA interacts with other proteins such as RNA polymerase and DnaA. Since the basic problem is one of reprogramming the chromosomes so that one chromosome is active and the other one is inactive in the appropriate cell-type, we are also studying proteins that modify DNA structure. In particular, we are studying a unique DNA methylation protein (that is also regulated by CtrA), and a new class of proteins that condense and decondense chromatin.
Selected Recent Publications
Rajagopalan M, Dziedzic R, Al Zayer M, Sankowska D, Ouimet MC, Bastedo DP, Marczynski GT, Madiraju MV. "Mycobacterium tuberculosis origin of replication and the promoter for immunodominant secreted antigen 85B are the targets of MtrA, the essential response regulator." J Biol Chem. 2010 May 21;285(21):15816-27. Epub 2010 Mar 11.PMID: 20223818 [PubMed - indexed for MEDLINE]
Spencer W, Siam R, Ouimet MC, Marczynski GT. "CtrA, a global response regulator, uses a distinct second category of weak DNA binding sites for cell cycle transcription control in Caulobacter crescentus." J Bacteriol. 2009 Sep;191(17):5458-70.Epub 2009 Jun 19.PMID: 19542275 [PubMed - indexed for MEDLINE]
Shaheen SM, Ouimet MC, Marczynski GT. "Comparative analysis of Caulobacter chromosome replication origins." Microbiology. 2009 Apr;155(Pt 4):1215-25.PMID: 19332823 [PubMed - indexed for MEDLINE]
Bastedo DP, Marczynski GT. "CtrA response regulator binding to the Caulobacter chromosome replication origin is required during nutrient and antibiotic stress as well as during cell cycle progression." Mol Microbiol. 2009 Apr;72(1):139-54. Epub 2009 Feb 11. Erratum in: Mol Microbiol. 2009 Apr;72(1):273. PMID: 19220749 [PubMed - indexed for MEDLINE]
Gorbatyuk B, Marczynski GT. "Regulated degradation of chromosome replication proteins DnaA and CtrA in Caulobacter crescentus." Mol Microbiol.2005 Feb;55(4):1233-45.PMID: 15686567 [PudMed - indexed for MEDLINE]
Siam R, Brassinga AK and Marczynski GT. "A dual binding site for integration host factor and the response regulator CtrA inside the Caulobacter crescentus replication origin." J Bacteriol. 2003; 185: 5563-72.
Siam R, Marczynski GT. "Glutamate at the phosphorylation site of response regulator CtrA provides essential activities without increasing DNA binding." Nucleic Acids Res. 2003;31(6):1775-9.
Brassinga AK, Siam R, McSween W, Winkler H, Wood D, Marczynski GT. "Conserved response regulator CtrA and IHF binding sites in the alpha-proteobacteria Caulobacter crescentus and Rickettsia prowazekii chromosomal replication origins." J Bacteriol. 2002;184(20):5789-99.
Marczynski GT, Shapiro L. "Control of chromosome replication in caulobacter crescentus." Annu Rev Microbiol. 2002;56:625-56. Review.
Brassinga AK, Marczynski GT. "Replication intermediate analysis confirms that chromosomal replication origin initiates from an unusual intergenic region in Caulobacter crescentus." Nucleic Acids Res. 2001;29(21):4441-51.
Gorbatyuk B, Marczynski GT. "Physiological consequences of blocked Caulobacter crescentus dnaA expression, an essential DNA replication gene." Mol Microbiol. 2001;40(2):485-97.
Brassinga AK, Siam R, Marczynski GT. "Conserved gene cluster at replication origins of the alpha-proteobacteria Caulobacter crescentus and Rickettsia prowazekii." J Bacteriol. 2001;183(5):1824-9.
Ouimet MC, Marczynski GT. "Analysis of a cell-cycle promoter bound by a response regulator." J Mol Biol. 2000;302(4):761-75.
Ouimet MC, Marczynski GT. "Transcription reporters that shuttle cloned DNA between high-copy Escherichia coli plasmids and low-copy broad-host-range plasmids." Plasmid. 2000;44(2):152-62.
Siam, R. and Marczynski, G.T. Cell cycle regulator phosphorylation stimulates two distinct modes of binding at a chromosome replication origin. The EMBO Journal, v. 19(5), 2000, pp. 1138-1147.
Brassinga, A.K.C., Gorbatyuk, B., Ouimet, M.-C. and Marczynski,G.T. "Selective cell cycle transcription requires membrane synthesis in Caulobacter." The EMBO Journal, v. 19(4), 2000, pp. 702-709.
Marczynski, G.T. "Chromosome Methylation and the Measurement of Faithful, Once and only Once per Cell-Cycle, Chromosome Replication in Caulobacter crescentus." J. Bacteriol., v. 181, 1999, pp. 1984-1993.
Quon, K., Yang, B., Domian, I., Shapiro, L., and Marczynski, G. "Negative Control of Bacterial DNA Replication by a Cell-Cycle Regulatory Protein that Binds at the Chromosome Origin. developmentally regulated chromosome origin of replication uses essential transcription elements." Proc. Natl. Acad. Sci. USA, v. 95, 1998, pp. 120-125.
Quon, K. C., Marczynski, G. T., Shapiro, L. "Cell cycle control by an essential bacterial two-component signal transduction protein." Cell, v. 84, 1996, pp. 83-93