Search PubMed⌕ Search

Biomedical subjects

M Cannon

Publications and source records attributed to M Cannon.

At least 91 records · Page 5Linked to original sources
PubMed1984

Defective processing of ribosomal precursor RNA in Saccharomyces cerevisiae.

Saccharomyces cerevisiae (strain A224A) has an abnormal distribution of cytoplasmic ribosomal subunits when grown at 36 degrees C, with sucrose-gradient analysis of extracts revealing an apparent excess of material sedimenting at 60 S. This abnormality is not observed at either 23 degrees C or 30 degrees C. At 36 degrees C the defect(s) is expressed as a slowed conversion of 20 S ribosomal precursor RNA to mature 18 S rRNA, although the corresponding maturation of 27 S ribosomal precursor RNA to mature 25 S rRNA is normal. Studies on this yeast strain and on mutants derived from it may help to elucidate the role(s) of individual ribosomal components in controlling ribosome biogenesis in eukaryotes.

Centrifugation, Density Gradient↗
PubMed1983

The nif promoters of Klebsiella pneumoniae have a characteristic primary structure.

We have determined the precise point of transcription initiation for five nif (nitrogen fixation) operons of Klebsiella pneumoniae and sequenced the promoters. Our results show that nifF is transcribed in the opposite direction to that previously proposed for nif genes, that nifM is transcribed from two promoters, and that there is a promoter preceding nifU but not nifX, and we present a revised map of nif transcripts. The nif promoters have a characteristic structure of 26 bp located between positions--1 and --26 upstream of the site of transcription initiation: CTGG..8bp...TTGCA...9bp...Py(+1). This structure, which has two regions of conserved sequence, shows no homology to the "consensus promoter" of enteric bacteria. Our results suggest that the--10 homology is equivalent to a "Pribnow box" for promoters expressed under nitrogen-starved conditions and that the--23 homology confers activator specificity on the nif promoters.

Base Sequence↗
PubMed1982

Ribosome structure, maturation of ribosomal RNA and drug sensitivity in temperature-sensitive mutants of Saccharomyces cerevisiae.

Selected strains of Saccharomyces cerevisiae were mutagenized with nitrosoguanidine and temperature-sensitive mutants isolated. These mutants were screened by two-dimensional gel-electrophoresis for the presence of ribosomal proteins with altered mobility relative to parental preparations. Electrophoretic changes were detected in three mutants designated ts205, ts212 and ts417, with the alterations apparently the same in the three cases. All three mutants were more sensitive than were their parents to the antibiotics G418, hygromycin B and MDMP. Mutant ts212 has an abnormal distribution of native ribosomal subunits and appears to be defective in its assembly of the smaller subparticle.

Electrophoresis, Polyacrylamide Gel↗
PubMed1982

Inhibition, by trichothecene antibiotics, of brain protein synthesis and fever in rabbits.

1. To test further the hypothesis that brain protein synthesis is necessary for fever, three structurally similar trichothecene antibiotics were injected into the cerebral ventricles of rabbits. They were 3,15-diacetoxy-12-hydroxytrichothec-9-ene (DAHT), 3,15-didesacetyl-calonectrin (DDAC) and T-2 toxin. Their actions on hypothalamic incorporation of [14C]leucine and fever were compared. 2. DDAC (60 micrograms) and T-2 toxin (10 micrograms) strongly inhibited leucine incorporation and fever. DAHT (60 micrograms) did not diminish fever and had a smaller effect upon leucine incorporation. 3. The findings strengthen considerably earlier suggestions that brain protein synthesis is an essential step in pyrogenesis.

Animals↗
PubMed1982

Inhibition of protein synthesis in Saccharomyces cerevisiae by the 12,13-epoxytrichothecenes trichodermol, diacetoxyscirpenol and verrucarin A. Reversibility of the effects.

Inhibition of protein synthesis by trichodermol, diacetoxyscirpenol and verrucarin A in cells and spheroplasts of Saccharomyces cerevisiae was investigated. Inhibition was reversible for trichodermol and diacetoxyscirpenol, both drugs being removed from their target site(s) by washing, but was reversible for verrucarin A. These results are interpreted in relation to variations in chemical structure between these trichothecenes.

Antineoplastic Agents↗
PubMed1980

A trichodermin-resistant mutant of Saccharomyces cerevisiae with an abnormal distribution of native ribosomal subunits.

1. A yeast mutant (CLP-8), resistant at the ribosome level to the trichothecene antibiotic trichodermin, differs from its parent in having an unusual distribution of native ribosomal subunits. Sucrose gradient analysis of cytoplasmic extracts from this mutant revealed a large excess of material sedimenting at 60 S with little or no material sedimenting at 40 S. 2. The excess 609-S material consists predominantly of functionally active 60-S ribosomal subunits, as indicated by both analysis of ribosomal RNA and studies in vitro using a poly(U)-directed protein-synthesizing system. 3. Using the poly(U) system it was found that high-salt-washed particles derived from either the excess 60-S peak or 80-S ribosomes of CLP-8 exhibited very similar levels of resistance to the antibiotic fusarenon-X, a drug closely related chemically to trichodermin. The same level of resistance to fusarenon-X was also shown by high-salt-washed 60-S ribosomal particles obtained from a further trichodermin-resistant yeast strain (TR-1), although this strain has a normal distribution of native ribosomal subunits. In addition, both CLP-8 and TR-1 are equally resistant to inhibition of protein synthesis by trichothecene antibiotics, as assayed in vivo. 4. Genetic analysis of CLP-8 indicates that the trichodermin-resistant trait can be segregated from the lesion responsible for the inbalance of native ribosomal subunits. However, the latter defect is only expressed phenotypically in cells that retain the trichodermin-resistant character. 5. CLP-8 has a further defect in that both in vivo and in vitro it fails to generate native 40-S ribosomal subunits from 80-S particles. There may be a lesion in the protein factor normally required for this process.

Drug Resistance, Microbial↗
PubMed1979

The nature of the hydroxyapatite-binding site in salivary acidic proline-rich proteins.

Protein A and C, which are major components of the acidic proline-rich proteins in human saliva, were digested, before or after adsorption to hydroxyapatite, with alkaline phosphatase, trypsin, thermolysin and a proteinase preparation from salivary sediment. The results demonstrate that the binding site is located in the proline-poor N-terminal part of the protein, possibly between residues 3 and 25. Phosphoserine is necessary for maximal adsorption of the proteins to hydroxyapatite. When proteins A and C are adsorbed to hydroxyapatite before proteolytic digestion there is a protection of some of the susceptible bonds in the N-terminal part of the proteins and a gradual removal of the proline-rich C-terminal part. Thermolysin can cleave susceptible bonds in the part of the protein that remains bound to hydroxyapatite, but at least some of the resulting peptides are retained on the mineral. Since the ability of the proteins to inhibit hydroxyapatite formation and to bind calcium is located in the N-terminal proline-poor part, it is possible that these activities are retained after proteolytic digestion of the adsorbed proteins.

Adsorption↗
PubMed1979

Methylation of basic proteins in ribosomes from wild-type and thiostrepton-resistant strains of Bacillus megaterium and their electrophoretic analysis.

Ribosomes, radioactively labelled in vivo with both [1-14C]methionine and [methyl-3H]methionine, have been isolated from both wild-type and thiostrepton-resistant strains of Bacillus megaterium and their constituent proteins separated by two-dimensional gel electrophoresis. Ribosomes from the wild-type strain possess one basic protein that is extensively methylated. In contrast no such protein can be detected in ribosomes from the thiostrepton-resistant strain.

Anti-Bacterial Agents↗
PubMed1979

Effects of apramycin, a novel aminoglycoside antibiotic on bacterial protein synthesis.

1. The novel aminoglycoside antibiotic apramycin is shown to be a potent inhibitor of protein synthesis in bacteria both in vivo and in vitro. 2. In cell-free systems from Escherichia coli programmed with poly(U), apramycin induces translation errors, as assayed by incorporation of leucine, isoleucine and serine, although this effect occurs only to a limited extent. 3. Apramycin inhibits the translocation step of protein synthesis both in vivo, in protoplasts of Bacillus megaterium, and in vitro, in cell-free systems from E. coli. It is proposed that this is the primary inhibitory effect of the drug.

Anti-Bacterial Agents↗