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R Bambara

Publications and source records attributed to R Bambara.

5 recordsLinked to original sources
PubMed1985

An analysis of the decrease in the assayed level of charged bovine estrogen receptor observed at physiological ionic strength.

Lower assayed levels of heifer uterine estrogen receptor (ER) occur at physiologic ionic strength when ER is separated from [3H]estradiol by Dextran-coated charcoal treatments, or by gel filtration on Sephadex or polyacrylamide resins. The assayed level of charged ER in buffers containing 150-200 mM ionic strength is approximately one-half that of ER levels assayed in buffers either at 0-50 or 400-450 mM ionic strength. Treatment of ER with trypsin or molybdate eliminates this observed reduction. Evidence is presented that the decrease results from a preferential adsorption of ER to the assay resins at 150-200 mM ionic strength. This adsorption is likely to be mediated by a hydrophobic region of the ER, which is removed by trypsin cleavage.

Acrylic Resins↗
PubMed1975

On the processive mechanism of Escherichia coli DNA polymerase I.

A procedure has been developed to assess whether polymerization of nucleotides by DNA polymerases is processive, that is, whether a succession of polymerization steps occurs without release of the enzyme from the template. The method involves measurement of the ratio of deoxyguanylate to deocycytidylate incorporated in the course of replicating a segment of the right hand cohesive end of phage lambaDNA with the sequence 5'-G-G-G-C-G-G-C-G-3'. In the case of the Escherichia coli DNA polymerase I, each enzyme molecule completes synthesis of the sequence before dissociation occurs. Furthermore, at both 6 and 22 degrees, the polymerase remains bound to the lambdaDNA template after synthesis has completed. Template challenge experiments, in which the polymerase is allowed to begin synthesis in the presence of a molar excess of lambdaDNA before addition of a very large excess of calf thymus DNA, show that under the conditions used, productive binding of polymerase to lambdaDNA is a slow process requiring 1 to 2 hours. After synthesis has been completed, polymerase remains bound to the lambdaDNA in spite of the availability of new primer termini. The association, polymerization, and dissociation rates measured in these experiments suggest that the polymerization reaction catalyzed by DNA polymerase I is processive, and that hundreds of nucleotides may be polymerized between each association and dissociation.

Base Sequence↗
PubMed1975

DNA sequence analysis. Terminal sequences of bacteriophage phi80.

Sequences of the cohesive ends and the 3'-terminal regions of phi80 DNA have been determined. Sequences of the cohesive ends were obtained through the use of two standard methods. The first method involved the incorporation of all four labeled deoxyribonucleotides into the phi80 cohesive ends using DNA polymerase I. The DNA was then partially digested with micrococcal nuclease or pancreatic DNase. The products were separated by two-dimensional electrophoresis and characterized by composition, 3'-terminal, and nearest neighbor analyses. The second method involved partial incorporation using one, two, or three labeled deoxyribonucleotides followed by similar analyses. Sequences of the double-stranded regions adjacent to the cohesive ends were determined by three new methods. These methods were: (a) the DNA was specifically labeled at the 3' terminus and then partially degraded. Labeled oligonucleotide products were sequenced by their mobilities on various separation systems. (b) The cohesive ends were enlarged by limited degradation with exonuclease III. After this treatment, the DNA was partially repaired with labeled nucleotides, digested, and the products were analyzed. (c) A synthetic ologonucleotide primer was bound to phi80 DNA which had been repaired with DNA polymerase I, and then partially digested with lambda-exonuclease. The primer was extended into the region of interest by partial repair with labeled nucleotides. The extended primer was isolated and analyzed.

Base Sequence↗
PubMed1975

On the statistical significance of primary structural features found in DNA-protein interaction sites.

Probabilities of occurrence for a number of the symmetries and other sequence regularities found in DNA-protein interaction site sequences have been calculated for segments of random DNA sequence. Results show that many of the symmetrical and repetitive features seen in these interaction sites are likely to have occured by chance. Other features are so unlikely to have occurred by chance that they are probably involved in the DNA-protein interaction processes.

Amino Acid Sequence↗