Training:
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B.S., 1961: Yale University
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M.S., 1963: Pennsylvania State University
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Ph.D., 1965: Pennsylvania State University
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Post Doctoral, 1965-1967: University of Sussex, England
Description and summary of research focus of the laboratory:
Work in this laboratory continues a long interest with radiation induced cellular mutagenesis and DNA repair. A convenient and effective probe of fundamental processes that deal with abnormal molecular structures in DNA has been possible with E. coli bacteria and ultraviolet radiation (254 nm, UV). We have focused on several aspects of a UV-induced photoproduct in DNA important to mutagenesis, the cytosine-containing cyclobutane pyrimidine dimer: 5'-T<>C-3' (T=C). Our results associate T=C with the production of a specific mutation, a G:C to A:T transition in DNA, that alters one base in the anticodon of a glutamine tRNA gene in E. coli. A similar transition is commonly found in the p53 gene within human cells that are skin cancers associating this mutation with exposure to sun light. Cyclobutane pyrimidine dimers such as T=C block normal DNA replication and give rise to mutated DNA sequence via a specialized translesion mode of DNA replication. A point of interest is whether deamination of cytosine in T=C before translesion DNA replication is critical in the mechanism for these transition mutations. A separate issue regards the repair of T=C prior to translesion replication so that mutations at this photoproduct no longer occur. Studies in our laboratory have helped to define the existence of transcription-coupled nucleotide excision repair (in several cell types including E. coli and human) which accounts for a phenomenon termed 'Mutation Frequency Decline' by quickly removing T=C lesions in the transcribed DNA strand that would otherwise produce mutations during translesion replication. The T=C lesion in DNA also may be repaired by DNA photolyase, a monomeric enzyme that uses light energy to rearrange the molecular bonds of T=C returning the normal structure. Without light (in the dark), photolyase binds to T=C in DNA (allowing it to rotate from its normal conformation in DNA to a pocket in the photolyase protein). We find these dark complexes to dramatically reduce mutations even though the T=C structure is not repaired. Moreover, these complexes appear to encumber certain other modes of DNA repair and stimulate depolarization of the cell membrane when RexAB proteins are present in the cell. Continuation of these studies is planned to conclude mid-2002 when the lab will be closed upon the retirement of Dr. Bockrath.
Publications
Ruiz-Rubio, M., K. Yamamoto and R. Bockrath. 1988 An in vivo complex with DNA photolyase blocks UV mutagenesis targeted at a thymine-cytosine dimer in E. coli. J. Bacteriol. 170:5371-5374.
Li, B.-H., and R. Bockrath. 1995. Photolyase-dimer-DNA complexes and exclusion stimulation in Escherichia coli: Depolarization of the plasma membrane. Mol. Gen. Genet. 240:450-454.
Bockrath, R., and B.-H. Li. 1997. Photoreversal of UV-potentiated glutamine tRNA suppressor mutations in excision proficient E. coli. Mutat. Res. 383:231-242.
Bockrath, R. 1998. Transcription repair coupling in E. coli.In, DNA Damage and Repair: Vol. I, DNA Repair in Prokaryotes and Lower Eukaryotes, eds., Nickoloff, J.A., and Hockstra, M.F. Humana Press, Totowa, NJ, pp. 169-177.
Li, B.-H., A. Ebbert and R. Bockrath. 1999. Transcription-modulated repair in Escherichia coli evident with UV-induced mutation spectra in supF. J. Mol. Biol. 294:35-48.
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