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Biomedical subjects

F Spencer

Publications and source records attributed to F Spencer.

At least 55 records · Page 3Linked to original sources
PubMed1992

CTF4 (CHL15) mutants exhibit defective DNA metabolism in the yeast Saccharomyces cerevisiae.

We have analyzed the CTF4 (CHL15) gene, earlier identified in two screens for yeast mutants with increased rates of mitotic loss of chromosome III and artificial circular and linear chromosomes. Analysis of the segregation properties of circular minichromosomes and chromosome fragments indicated that sister chromatid loss (1:0 segregation) is the predominant mode of chromosome destabilization in ctf4 mutants, though nondisjunction events (2:0 segregation) also occur at an increased rate. Both inter- and intrachromosomal mitotic recombination levels are elevated in ctf4 mutants, whereas spontaneous mutation to canavanine resistance was not elevated. A genomic clone of CTF4 was isolated and used to map its physical and genetic positions on chromosome XVI. Nucleotide sequence analysis of CTF4 revealed a 2.8-kb open reading frame with a 105-kDa predicted protein sequence. The CTF4 DNA sequence is identical to that of POB1, characterized as a gene encoding a protein that associates in vitro with DNA polymerase alpha. At the N-terminal region of the protein sequence, zinc finger motifs which define potential DNA-binding domains were found. The C-terminal region of the predicted protein displayed similarity to sequences of regulatory proteins known as the helix-loop-helix proteins. Data on the effects of a frameshift mutation suggest that the helix-loop-helix domain is essential for CTF4 function. Analysis of sequences upstream of the CTF4 open reading frame revealed the presence of a hexamer element, ACGCGT, a sequence associated with many DNA metabolism genes in budding yeasts. Disruption of the coding sequence of CTF4 did not result in inviability, indicating that the CTF4 gene is nonessential for mitotic cell division. However, ctf4 mutants exhibit an accumulation of large budded cells with the nucleus in the neck. ctf4 rad52 double mutants grew very slowly and produced extremely high levels (50%) of inviable cell division products compared with either single mutant alone, which is consistent with a role for CTF4 in DNA metabolism.

Amino Acid Sequence↗
PubMed1990

The CHL 1 (CTF 1) gene product of Saccharomyces cerevisiae is important for chromosome transmission and normal cell cycle progression in G2/M.

We have analyzed the CTF1 gene, identified in a screen for mutants with decreased chromosome transmission fidelity and shown to correspond to the previously identified chl1 mutation. Chl1 null mutants exhibited a 200-fold increase in the rate of chromosome III missegregation per cell division, and near wild-type rates of marker homozygosis on this chromosome by mitotic recombination. Analysis of the segregation of a marker chromosome indicated that sister chromatid loss (1:0 segregation) and sister chromatid non-disjunction (2:0 segregation) contributed equally to chromosome missegregation. A genomic clone of CHL1 was isolated and used to map its physical position on chromosome XVI. Nucleotide sequence analysis of CHL1 revealed a 2.6 kb open reading frame with a 99 kd predicted protein sequence that contained two PEST sequences and was 23% identical to the coding region of a nucleotide excision repair gene, RAD3. Domains of homology between these two predicted protein sequences included a helix-turn-helix motif and an ATP binding site containing a helicase consensus. Mutants lacking the CHL1 gene product are viable and display two striking, and perhaps interrelated, phenotypes: extreme chromosome instability and a delay in cell cycle progression in G2/M. This delay is independent of the cell cycle checkpoint that requires the function of the RAD9 gene.

Alleles↗
PubMed1990

Mitotic chromosome transmission fidelity mutants in Saccharomyces cerevisiae.

We have isolated 136 independent mutations in haploid yeast strains that exhibit decreased chromosome transmission fidelity in mitosis. Eighty-five percent of the mutations are recessive and 15% are partially dominant. Complementation analysis between MATa and MAT alpha isolates identifies 11 chromosome transmission fidelity (CTF) complementation groups, the largest of which is identical to CHL1. For 49 independent mutations, no corresponding allele has been recovered in the opposite mating type. The initial screen monitored the stability of a centromere-linked color marker on a nonessential yeast chromosome fragment; the mitotic inheritance of natural yeast chromosome III is also affected by the ctf mutations. Of the 136 isolates identified, seven were inviable at 37 degrees and five were inviable at 11 degrees. In all cases tested, these temperature conditional lethalities cosegregated with the chromosome instability phenotype. Five additional complementation groups (ctf12 through ctf16) have been defined by complementation analysis of the mutations causing inviability at 37 degrees. Twenty-three of the 136 isolates exhibited growth defects at concentrations of benomyl permissive for the parent strain, and nine appeared to be tolerant of inhibitory levels of benomyl. All of the mutant strains showed normal sensitivity to ultraviolet and gamma-irradiation. Further characterization of these mutant strains will describe the functions of gene products crucial to the successful execution of processes required for aspects of the chromosome cycle that are important for chromosome transmission fidelity in mitosis.

Benomyl↗
PubMed1988

Platinum levels in murine tumor following intraperitoneal administration of cisplatin or paraplatin.

To design protocols for exploitation of the potential for interaction among the platinum (Pt) chemotherapeutic agents cisplatin and paraplatin and radiation therapy, we measured levels of total platinum in a transplantable murine mammary adenocarcinoma (MTG-B) at different times after ip injection of platinum drugs and in various regimens. Cisplatin (20 mg/kg body weight) or paraplatin (60 or 120 mg/kg body weight) were injected ip in female C3H/HeJ mice bearing MTG-B of about 1 cm diameter. At various times after injection, tumors were removed and processed for acid digestion and total platinum analysis by atomic absorption spectrometry with a graphite furnace. The results of these experiments indicate that intratumoral Pt levels 15 minutes postinjection are higher than at 5 or 30 minutes. At 30 minutes, the Pt concentrations are of the magnitudes of 30 and 50 microM for cisplatin and paraplatin, respectively, that, when added to cells in vitro in combination with radiation therapy, produce the potentiation of cell killing. In addition, for paraplatin, intratumoral Pt levels at 30 minutes following an ip injection are approximately doubled if the tumors receive localized radiotherapy of 20 Gy immediately prior to injection of the drug. This apparent modification of paraplatin pharmacokinetics by radiotherapy might account for some of the supra-additive therapeutic potentiation in MTG-B reported for paraplatin added after irradiation.

Animals↗
PubMed1986

Long-term follow-up after mitral valve reconstruction: incidence of postoperative left ventricular outflow obstruction.

Reconstructive surgery of the mitral valve has been an alternative to mitral valve replacement in patients with mitral regurgitation. Previously, we reported on postoperative left ventricular outflow tract obstruction associated with systolic anterior motion of the anterior mitral leaflet. The current study was designed to evaluate the incidence of this complication and the long-term results of mitral valve reconstructive surgery. Sixty-five patients, aged 19 to 78 years, had mitral valve reconstructive surgery. Two patients died perioperatively, and three died late after surgery. The 60 surviving patients were studied by M mode, two-dimensional, and Doppler echocardiography 1 to 55 months postoperatively (mean 21). Fifty patients had no evidence of postoperative mitral regurgitation, two patients had moderate mitral regurgitation, three patients had mild mitral regurgitation, and five patients had trace mitral regurgitation. No significant mitral stenosis was detected in any patient postoperatively. After surgery, the diameter of the left ventricular outflow tract was significantly smaller than that before surgery. The echocardiograms of six patients showed abnormal systolic anterior motion of the anterior mitral leaflet that was not observed preoperatively. Doppler echocardiography demonstrated pressure gradients across the left ventricular outflow tract between 10 and 64 mm Hg. Inhalation of amyl nitrite increased these gradients. An additional patient who had systolic anterior motion but no gradient developed a 36 mm Hg gradient after inhalation of amyl nitrite. The remaining patients had no gradient induced by amyl nitrite. Abnormal systolic anterior motion of the anterior mitral leaflet may be surgically induced by changes in left ventricular geometry and the size of the left ventricular outflow tract during systole.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1981

Importance of topical hypothermia to ensure uniform myocardial cooling during coronary artery bypass.

Recent reports have suggested that the delivery of cardioplegia to regional myocardium is impaired in patients with severe coronary artery disease. This study was designed to determine whether or not topical hypothermia is a necessary adjunct to systemic hypothermia and potassium cardioplegia to provide adequate cooling in regional myocardium supplied by stenotic or occluded coronary arteries. Twenty-two patients ranging in age from 47 to 68 years were included in the study. Patients were placed on bypass and cooled to 28 degrees C. Temperature was measured over the right and left coronary artery distributions. The aorta was then cross-clamped and 1,000 cc of potassium blood cardioplegia, 5.7 degrees to 11 degrees C (mean 8.7 degrees), was infused into the aortic root at a mean pressure of 99 mmHg. Temperature was measured and 6 L of cold electrolyte (Plasma-lyte) solution, 2.3 degrees to 5.1 degrees C (mean 3.5) was poured over the heart into the pericardial well. The temperature measurements were then repeated. Myocardial temperature in regional myocardium supplied by normal coronary arteries after the injection of cardioplegia was less than 15 degrees C. However myocardium distal to a severe stenosis or complete occlusion was significantly warmer (p less than 0.001). Topical hypothermia reduced myocardial temperature to less than 15 degrees C in regional myocardium supplied by severely diseased vessels (p less than 0.001). These data demonstrate that the combination of systemic hypothermia and potassium cardioplegia alone does not provide adequate myocardial cooling in patients with severe coronary artery disease and emphasize the need for intraoperative myocardial temperature monitoring to ensure optimal protection during the ischemic period.

Aged↗