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D W Bean

Publications and source records attributed to D W Bean.

12 recordsLinked to original sources
PubMed1997

Identification of the gene encoding scHelI, a DNA helicase from Saccharomyces cerevisiae.

The gene encoding scHelI, a previously characterized DNA helicase from Saccharomyces cerevisiae, has been identified as YER176w, an open reading frame on chromosome V. The gene has been named HEL1 to indicate the DNA helicase activity of the gene product. HEL1 was identified by screening a lambda gt11 yeast protein expression library with antiserum to purified scHelI. Several independent immunopositive clones were isolated and shown to contain portions of HEL1 either by sequencing or by hybridization to a probe containing HEL1 sequences. The HEL1 open reading frame includes the seven conserved helicase motifs, consistent with the DNA helicase activity of scHelI, and the predicted size of the protein is in agreement with the size of purified scHelI. Partially purified cellular extracts from a hel1 deletion mutant strain did not contain scHelI activity. Homology searches revealed protein sequence homology between HEL1 and two previously identified and biochemically characterized yeast helicases, encoded by the DNA2 and UPF1 genes. Haploid hel1 deletion strains were constructed and shown to be viable with growth rates equivalent to those of parental strains. These strains did not differ from the parental strains in ultraviolet light sensitivity or the generation of petite colonies. Furthermore, these haploid deletion strains were capable for mating, the resultant diploid homozygous mutants were viable, capable of sporulation, and the spores displayed no reduction in viability.

Amino Acid Sequence↗
PubMed1995

Acute cholecystitis in an animal model: findings on color Doppler sonography.

OBJECTIVE: The purpose of our study was to evaluate the color Doppler findings of acute cholecystitis in a controlled canine model. MATERIALS AND METHODS: Fourteen animals had a laparotomy: cystic duct ligation was done in eight, and incision with closure was performed in six control subjects. Animals were scanned in a blinded fashion preoperatively, immediately postoperatively, and on postoperative days 1-5. On postoperative day 5, a hepatobiliary scan was done with 2 mCi (74 MBq) 99mTc-mebrofenin. Blinded histopathology was performed and correlated with imaging. RESULTS: Flow was seen in the wall of each gallbladder at some point during the postoperative course, demonstrating vascular patency. Hepatobiliary scintigraphy confirmed cystic duct status in 12 cases; two animals died before radionuclide imaging was complete. Color Doppler signal decreased in the gallbladder wall in ligated dogs from postoperative day 1 to postoperative day 3 (p = .03 versus controls at postoperative day 2) and increasingly returned by postoperative day 5. Hyperemia was seen in only two cases (both with severe necrotizing cholecystitis) and only at postoperative day 5. Although not statistically significant, a weak trend of increasing flow with more severe pathologic grades of cholecystitis was observed (p = .20). CONCLUSIONS: In this animal model, loss of vascular signal (not hyperemia) at postoperative day 2 was the finding to diagnose early acute cholecystitis, although lack of flow can also be seen in some normal subjects. Flow tended to return by postoperative day 5, and it increased in some of the more severe cases of cholecystitis. Hyperemia was a somewhat useful sign of acute necrotizing cholecystitis.

Acute Disease↗
PubMed1994

DNA helicases: enzymes with essential roles in all aspects of DNA metabolism.

DNA helicases catalyze the disruption of the hydrogen bonds that hold the two strands of double-stranded DNA together. This energy-requiring unwinding reaction results in the formation of the single-stranded DNA required as a template or reaction intermediate in DNA replication, repair and recombination. A combination of biochemical and genetic studies have been used to probe and define the roles of the multiple DNA helicases found in E. coli. This work and similar efforts in eukaryotic cells, although far from complete, have established that DNA helicases are essential components of the machinery that interacts with the DNA molecule.

Animals↗
PubMed1993

Purification and characterization of a DNA helicase from Saccharomyces cerevisiae.

A novel DNA helicase, scHelI, has been purified from whole cell extracts of Saccharomyces cerevisiae using biochemical assays to monitor the fractionation. The enzyme unwinds partial duplex DNA substrates, as long as 343 base pairs in length, in a reaction that is dependent on either ATP or dATP hydrolysis. scHelI also catalyzes a single-stranded DNA-dependent ATP hydrolysis reaction; the apparent Km for ATP is 325 microM. The unwinding reaction on circular partial duplex substrates is biphasic, with a fast component occurring within 5 min of the initiation of the reaction and a slow component continuing to 60 min. This is in contrast to the ATP hydrolysis reaction, which exhibits linear kinetics for 60 min. The direction of the unwinding reaction is 5' to 3' with respect to the strand of DNA on which the enzyme is bound. The unwinding reaction is strongly stimulated by the addition of Escherichia coli single-stranded DNA-binding protein when long partial duplex substrates are used. The enzymatic activity of scHelI copurifies with a polypeptide of 135 kDa as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The polypeptide sediments as a monomer in a glycerol gradient in the presence of 0.2 M NaCl.

Adenosine Triphosphatases↗