Chad A. Robertson

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The covalent joining of topoisomerases to DNA is normally a transient step in the reaction cycle of these important enzymes. However, under a variety of circumstances, the covalent complex is converted to a long-lived or dead-end product that can result in chromosome breakage and cell death. We have discovered and partially purified an enzyme that(More)
Covalent intermediates between topoisomerase I and DNA can become dead-end complexes that lead to cell death. Here, the isolation of the gene for an enzyme that can hydrolyze the bond between this protein and DNA is described. Enzyme-defective mutants of yeast are hypersensitive to treatments that increase the amount of covalent complexes, indicative of(More)
BACKGROUND The covalent linkage between DNA and the active site tyrosine of topoisomerase I can be stabilized by chemotherapeutic agents, adjacent DNA lesions, or mutational defects in the topoisomerase itself. Following collision with a replication fork, the covalent complex can be converted to a double-strand break. Tdp1, an enzyme that can hydrolyse the(More)
Integration host factor (IHF) is a small, basic protein that is needed for efficient recombination of bacteriophage lambda, as well as for other host and viral functions. We have constructed strains in which the two subunits of IHF, encoded by the himA and hip genes of Escherichia coli, are expressed under the control of the lambda rho L promoter. Separate(More)
A purified preparation of the Escherichia coli integration host factor (IHF) displays two polypeptides of apparent molecular weight 11,000 and 9,500 when analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Under nondenaturing conditions, IHF appears to exist as a 1:1 complex of these two polypeptides. Integrative(More)
Escherichia coli integration host factor (IHF) is a small basic protein that is required for efficient integrative recombination of bacteriophage lambda. IHF binds specifically to sequences within attP, the site in bacteriophage lambda that undergoes recombination. It has been suggested that the binding of IHF creates bends in DNA so as to help attP(More)
Lambda's Int protein acts as a specific topoisomerase at attachment sites, the DNA segments that are required for site-specific recombination. Int cleaves each strand of an attachment site at a unique place and creates strand exchanges by joining broken ends from two different parents. To study the action of Int topoisomerase in more detail, heteroduplex(More)
Software has been developed to help engineers visualize the gamuts of color hardcopy devices. Software modules have been written so that color gamuts and color space transformations can be explored using a scientific visualization program. Tools have been created that allow the user to accentuate the differences between gamuts and to interact with the(More)
Glycerol-3-phosphate acyltransferase has been purified from the post-microsomal supernatant of cocoa seeds using differential ammonium sulfate solubility along with anion exchange and gel filtration chromatography. Chromatofocusing and isoelectric focusing revealed a series of proteins with acyltransferase activity having isoelectric points close to 5.2.(More)
The efficiency of estimating allelic and genotypic frequencies at allozyme loci can often be increased by running more than one individual simultaneously in each sample slot in a gel. Increased precision in estimating allelic frequencies is always possible if Hardy-Weinberg proportions can be assumed. However, if Hardy-Weinberg cannot be assumed, estimates(More)