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Contact information Recent publications Curriculum vitae Laboratory of Molecular Biology |
Biography: Dr. Ding Jun Jin received his Ph.D. from the Department of Molecular Biology at the University of Wisconsin-Madison in 1988. He studied RNA polymerase as a Research Associate with Dr. Carol A. Gross. Dr. Jin joined Laboratory of Molecular Biology, NCI, as an independent investigator in 1991.Research overview: RNA polymerase (RNAP) and its associated proteins will be studied by combining biochemical and genetic approaches. Important domains in RNAP will be identified by isolating and characterizing mutant RNAPs that have altered particular functions in transcription. Transcription mechanisms will be dissected by comparing biochemical properties of wild-type and mutant RNAPs at specific steps in the transcription process. Currently, we have focused on the following studies:Interaction between RNAP and stringently controlled promoters. During rapid growth, the majority of RNA polymerase (RNAP) molecules inside the E. coli cell are engaged in transcription of a very small set of genes in the genome, most of which encode translational machinery such as ribosomal RNA, transfer RNA, and ribosomal proteins. However, under nutrient-limiting conditions, a process termed the stringent response, the expression of the above genes called stringent genes, is dramatically reduced. To understand how the expression of stringent genes is coordinately regulated, we analyzed the interactions between RNAP (both wild type and mutants that have altered the expression of stringent genes) and several stringent promoters using a purified system. We identified a unique feature of stringent promoters: the initiation complexes of these promoters are intrinsically unstable and can alternate between relatively stable and metastable states depending on the superhelicity of the DNA template. We also identified a class of RNAP mutants that behaved like "stringent" RNAPs even in the absence of the stringent response in vivo. In vitro, these mutant RNAPs formed extremely unstable initiation complexes specifically at stringent promoters. We propose that modulation of the stability of the initiation complexes of stringent promoters is a key element in regulation of stringent genes and suggest that the stability of initiation complexes is coupled to the transcription of stringent promoters because transcription and local supercoiling of the DNA template are interrelated. Currently, we are identifying the cis and trans factors that modulate the stability of the initiation complexes of stringent promoters, as well as the regions in RNAP that are important for such interactions.Interplay between core RNAP and sigma factors. Interaction between core RNAP and different sigma factors forming a holoenzyme is the first step in transcription initiation. We have studied this interaction by mutational analysis. We found that altering the amount of a major sigma factor will perturb the equilibrium of different forms of holoenzyme, reflecting the competition of different sigma factors for binding to core RNAP. We also found that rpoH mutations, which affected different regions of the sigma-32, have altered the affinity to core RNAP indicating that multiple sites in the sigma factor are involved in binding to core RNAP. Some sigma mutations that are defective in binding to core RNAP lead to temperature-sensitive for cell growth. We have isolated several second-site temperature-resistant suppressors. Some of these suppressors mutations are located in the rpoBC genes encoding the two largest subunits of core RNAP. These suppressors mutations will be further analyzed.Regulation and function of RapA. Recently, we have identified a novel E. coli RNA polymerase (RNAP)-associated protein, an ATPase named RapA. Almost all of this 110-kDa protein in the cell copurifies with RNAP holoenzyme as a 1:1 complex. Purified to homogeneity, RapA also forms a stable complex with RNAP, as if it were a subunit of RNAP. The ATPase activity of RapA is stimulated by binding to RNAP, thus, RapA and RNAP interact physically as well as functionally. Interestingly, RapA is a homolog of the SWI/SNF family of eukaryotic proteins whose members are involved in transcription activation, nucleosome remodeling, and DNA repair. The interaction between RNAP and RapA will be further studied. The regulation of the RapA gene and its function inside cell will be analyzed.Recent Publications: |
Contact Information: Laboratory of Molecular Biology,NCI, NIHBuilding 37, Room 2E1437 CONVENT DR MSC 4255BETHESDA MD 20892-4255Phone: 301-496-3209Fax:301-402-1344Email: djjin@helix.nih.gov
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