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Biomedical subjects

M Jackson

Publications and source records attributed to M Jackson.

At least 379 records · Page 21Linked to original sources
PubMed1975

A deletion map of cyc1 mutants and its correspondence to mutationally altered iso-1-cytochromes c of yeast.

Mutants arising spontaneously from sporulated cultures of certain strains of yeast, Saccharomyces cerevisiae, contained deletions of the CYC1 gene which controls the primary structure of iso-1-cytochrome c. At least 60 different kinds of deletions were uncovered among the 104 deletions examined and these ranged in length from those encompassing only two adjacent point mutants to those encompassing at least the entire CYC1 gene. X-ray-induced recombination rates of crosses involving these deletions and cyc1 point mutants resulted in the assignment of 211 point mutants to 47 mutational sites and made it possible to unambiguously order 40 of these 47 sites. Except for one mutant, cyc1-15, there was a strict colinear relationship between the deletion map and the positions of 13 sites that were previously determined by amino acid alterations in iso-1-cytochromes c from intragenic revertants.

Chromosome Aberrations↗
PubMed1975

Mapping and gene conversion studies with the structural gene for iso-1-cytochrome C in yeast.

We have investigated the order of the four genes cyc1, rad7, SUP4, and cdc8 which form a tightly linked cluster on the right arm of chromosome X in the yeast Saccharomyces cerevisiae. Crossing over and coconversion data from tetrad analysis established the gene order to be centromere-cyc1-rad7-SUP4. Also cdc8 appeared to be distal to SUP4 on the basis of crossovers that were associated with conversion of SUP4. The frequencies of recombination and the occurrence of coconversions suggest that these four genes are contiguous or at least nearly so. Gene-conversion frequencies for several cyc1 alleles were studied, including cyc1-1, a deletion of the whole gene that extends into the rad7 locus. The cyc1-1 deletion was found to be capable of conversion, though at a frequency some fivefold less than the other alleles studied, and both 3:1 and 1:3 events were detected. In general 1:3 and 3:1 conversion events were equally frequent at all loci studied, and approximately 50% of conversions were accompanied by reciprocal recombination for flanking markers. The orientation of the cyc1 gene could not be clearly deduced from the behavior of the distal marker SUP4 in wild-type recombinants that arose from diploids heteroallelic for cyc1 mutations.

Chromosome Mapping↗
PubMed1974

Mutants of yeast defective in iso-1-cytochrome c.

A medium containing chlorolactate has been devised to enrich for mutants that are unable to utilize lactate for growth, and therefore that may be defective in cytochrome c. Complementation tests of 6,520 chlorolactate-resistant mutants that were obtained spontaneously or induced with UV, ICR-170, or nitrosoimidazolidone resulted in the identification of 195 mutations at the cyc1 locus, which controls the primary structure of iso-1-cytochrome c. These 195 mutants, with 16 cyc1 mutants previously isolated, were examined for total cytochrome c by spectroscopic methods, growth on lactate medium, suppressibility by defined nonsense suppressors, mutational sites by x-ray-induced recombination, ability to revert, and in 86 cases, whether intragenic revertants contain altered iso-1-cytochrome c. Except for the deletion mutant cyc1-1, all of the mutants appeared to contain single-site mutations that could be assigned to at least 35 different sites within the gene. The cyc1 mutants either completely lacked iso-1-cytochrome c or contained iso-1- cytochromes c that were completely or partially nonfunctional. In spite of the fact that the cyc1 mutants obtained by the chlorolactate procedure were selected on the basis of defective function, 68% appeared to completely lack iso-1-cytochrome c. The remaining cyc1 mutants contained below normal amounts of iso-1-cytochromes c. Studies at several incubation temperatures indicated that these nonfunctional iso-1-cytochromes c were thermolabile. It is suggested that the predominant means for abolishing iso-1-cytochrome c by mutations are either through a complete loss, such as produced by chain terminating codons, or impairments through drastic changes of tertiary structure which lead to instability and thermolability.

Acridines↗
PubMed1973

The nature of polydisperse ribonucleic acid in plants.

The aggregation of ribosomal RNA species during chromatography on methylated albumin on kieselguhr was decreased from 50 to 15% by the lower salt concentrations made possible by the use of higher pH values. The polydisperse RNA was resolved into two fractions. About 50% was eluted with the rRNA whereas the remainder was bound to the column, and was recovered only by solubilization of the methylated albumin. Both fractions of polydisperse RNA were similar in size range, but the bound fraction was considerably richer in AMP. No D-RNA (DNA-like RNA) peak was resolved under these conditions of column fractionation. However, the properties of the bound RNA were consistent with it containing both D-RNA and TB-RNA (tenaciously bound RNA). The relationship between these two fractions of AMP-rich RNA was considered. The bound RNA and ribosomal RNA responded differently to various treatments. The salt concentration required to elute ribosomal RNA was halved by increasing the pH of the fractionation, but the amount of bound RNA was in fact increased. Denaturation by hot urea decreased the binding of ribosomal RNA to the methylated albumin, but did not facilitate elution of bound RNA. The high affinity between the AMP-rich polydisperse RNA and the methylated albumin does not therefore appear to arise for the secondary structure conferred by the high AMP content.

Adenosine Monophosphate↗
PubMed1972

Cephamycins, a new family of beta-lactam antibiotics. I. Production by actinomycetes, including Streptomyces lactamdurans sp. n.

A number of actinomycetes isolated from soil were found to produce one or more members of a new family of antibiotics, the cephamycins, which are structurally related to cephalosporin C. The cephamycins were produced in submerged fermentation in a wide variety of media by one or more of eight different species of Streptomyces, including a newly described species, S. lactamdurans. These antibiotics exhibit antibacterial activity against a broad spectrum of bacteria which includes many that are resistant to the cephalosporins and penicillins.

Actinomyces↗