Our Science – Chattoraj Website

Dhruba K. Chattoraj, Ph.D.

Laboratory of Biochemistry and Molecular Biology Head, Control of DNA Replication Section Senior Investigator Laboratory of Biochemistry, NCI/CCR 37 Convent Drive Building 37, Room 6044, MSC 4260 Bethesda, MD 20892-4255 Phone:   301-496-9194 Fax:   301-480-1493 E-Mail:   chattoraj@nih.gov

Biography

Dr. Dhruba Chattoraj received his Ph.D. in biophysics in 1970 from the University of Calcutta, India, where he studied chromatin structure. As a postdoctoral associate, he studied nucleoprotein interactions involved in phage DNA replication and recombination at the University of Wisconsin with Dr. Ross Inman, and at the University of Oregon with Dr. Frank Stahl. His current research interest is on replication and segregation of chromosomes in the bacterial cell cycle. He is editor-in-chief of Plasmid, a member of the editorial board of J. Bacteriology, and a fellow of the American Academy of Microbiology.

Research

Chromosome Maintenance in Bacteria

Our interest is in mechanisms that control chromosome replication and segregation. These mechanisms are widely shared among organisms and are fundamental to their growth and development. Subversion of the mechanisms causes aneuploidy, the hallmark of cancer cells. The importance of genome stability, therefore, can hardly be overstated. A greater understanding of the mechanisms operating in bacterial models should be of general interest and guide the rational development of therapeutics for diseases, particularly bacterial infections.

Prokaryotic genomes usually consist of a single circular replicon. However, it is now becoming clear from genome sequencing projects that bacteria can also have more than one chromosome, as in eukaryotes. This has provided an opportunity to study how replication and segregation are coordinated among the chromosomes in organisms which are easily tractable genetically. We are studying these processes in Vibrio cholerae, which has two chromosomes (chrI and chrII).

Coordination of replication

The origin of chrI is nearly identical to the well-studied origin of E. coli. The origin of chrII is different and is under the control of a novel regulatory gene rctA, which is transcribed but not translated. We find that the transcription of rctA actually inactivates the function of the gene. This has provided a handle to conditionally regulate the gene. Our initial studies show that stopping transcription of rctA makes it a strong negative regulator of chrII replication. Blocking chrII replication generates chrII-less cells but does not inhibit chrI replication. This indicates that there may not exist a check-point control to coordinate replication of the two chromosomes.

Structure-function analysis of RctB protein

The initiator protein for chrII replication, RctB, is larger than most of the known replication initiators of bacteria and is likely to have novel features. This has prompted us to embark on a systematic structure-function analysis of the protein. The protein binds to disparate specific sequences both for initiation of replication and its regulation. The binding activity is also modulated by chaperone proteins, suggesting the importance of DNA binding in the regulation of replication.

Chromosome dynamics

One of the exciting developments in studies of bacterial chromosome maintenance is the ability to visualize genes and proteins in real time by fluorescence microscopy. We are following the dynamics of different chromosomal loci in the cell cycle to understand where the two chromosomes initiate their replication, how the daughter chromosomes segregate and the temporal relationship of termination of DNA replication and cell division. We are also studying if centromeres are used in chromosome segregation, as in eukaryotes. The fluorescence microscopic studies are complemented with flow cytometric studies to derive different cell cycle parameters.

Evolution of divided genomes

The origin of multipartite genomes is an evolutionary interesting question. Management of multiple chromosomes adds to the regulatory burden of the cell, which must be offset by growth advantages that remain to be understood. We are testing several models. Bioinformatics analysis indicates that the chrII originated from a plasmid. We are most interested to know how far the basic tenets of plasmid replication: random replication timing in the cell cycle and random choice of plasmid copies for replication apply to chrII.

This page was last updated on 7/21/2008.