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C K Mathews

Publications and source records attributed to C K Mathews.

107 records · Page 6Linked to original sources
PubMed1971

Identity of genes coding for soluble and structural dihydrofolate reductases in bacteriophage T4.

By recombination between bacteriophage T4 wh2, a dihydrofolate reductaseless mutant, and T6, I have prepared T4 wh(T6), a T4 strain which codes for the T6-specific soluble dihydrofolate reductase. This strain has the heat sensitivity of T6, not T4, which provides direct evidence that the wh gene codes for both the soluble dihydrofolate reductase and the structural dihydrofolate reductase which is a constituent of T-even phage tail plates.

Adsorption↗
PubMed1971

T-even bacteriophage-tolerant mutants of Escherichia coli B. II. Nucleic acid metabolism.

T-even bacteriophage-tolerant mutants are strains of Escherichia coli which can adsorb T-even phages but cannot support the growth of infective virus. Under some conditions, the infected cells are not killed. Mutant cells infected by phage T6 are able to carry out several metabolic functions associated with normal virus development, including arrest of bacterial nucleic acid and protein synthesis, incorporation of isotopic precursors into viral nucleic acids and proteins, synthesis of early enzymes of deoxyribonucleic acid (DNA) metabolism, formation of rapidly sedimenting DNA intermediates, and formation of normal levels of early and late messenger ribonucleic acid species. Phage are unable to mutate to forms capable of growth on these mutants. The nature of the biochemical alteration leading to tolerance is still unknown.

Adsorption↗
PubMed1970

Intracellular inactivation of bacteriophage T4 early deoxyribonucleic acid.

As previously shown, a small amount of polynucleotide material is added to parental T4 deoxyribonucleic acid (DNA) molecules within the first 5 min of infection. I have asked whether this process is essential for phage replication. Two approaches-one involving decay of (32)P incorporated into this "early DNA" and the other involving photoinactivation of bromodeoxyuridine-containing early DNA-indicate that it is.

Bromodeoxyuridine↗
PubMed1970

T-even bacteriophage-tolerant mutants of Escherichia coli B. I. Isolation and preliminary characterization.

A general procedure is described for isolation of T-even phage-tolerant mutants of Escherichia coli. Two such mutants of E. coli B have been examined in some detail. These mutants adsorb T-even phages but are unable to release viable progeny. Under certain conditions, viability of the cells is completely unaffected by phage infection in one mutant, and there is but a slight decrease in colony-forming ability in the other. Phage deoxyribonucleic acid (DNA) is injected into these cells, as shown by the formation of phage-specific enzymes, but it is not degraded to acid-soluble material. Some phage DNA replication occurs in both strains. The mutants are both more resistant to ultraviolet light than is the parent strain.

Adsorption↗
PubMed1967

Control of bacteriophage-induced enzyme synthesis in cells infected with a temperature-sensitive mutant.

The timing of "early" and "late" protein synthesis in Escherichia coli infected with T-even bacteriophage was studied with a temperature-sensitive phage mutant, T4 tsL13. This strain was completely unable to direct the synthesis of phage deoxyribonucleic acid (DNA) at 44 C because it makes a deoxycytidylate hydroxymethylase which cannot act at that temperature. However, the mutant did multiply normally at 30 C. No detectable formation of the late protein, lysozyme, occurred at 44 C, in agreement with the idea, proposed by several workers, that DNA replication is necessary for activation of late genetic functions. However, the formation of an early enzyme, thymidylate synthetase, was shut off at about 10 min, as in normal infection. This implied that separate mechanisms were responsible for cessation of early functions and activation of late ones. That the infected cell at 44 C retained the capacity for synthesis of early enzymes was shown by the fact that DNA synthesis occurred after a culture was transferred from 44 to 30 C as late as 30 min after infection. This synthesis was inhibited by chloramphenicol, indicating that de novo synthesis of an early enzyme can take place at a late period in development. It is suggested that cells infected under normal conditions maintained an appreciable rate of early enzyme synthesis throughout the course of infection.

Carbon Isotopes↗
PubMed1967

Growth of a dihydrofolate reductaseless mutant of bacteriophage T4.

A mutant of bacteriophage T4 was isolated which was unable to induce virus-specific dihydrofolate reductase in infected cells. The mutant was able to form several other early enzymes of pyrimidine metabolism. Growth of the mutant in a wild-type host, Escherichia coli B, was compared with that of the parent strain, T4BO(1), and T4td8, a mutant which lacks the ability to induce thymidylate synthetase. Growth studies were carried out in minimal medium, which gave higher growth rates and phage yields than the supplemented media used in previous studies. The reductase mutant formed deoxyribonucleic acid and plaque-forming particles at a rate slightly higher than the synthetase mutant but 1.5-to 2-fold lower than that of the wild-type phage under all conditions studied. The addition of thymine to a culture infected by the mutant increased the growth rate significantly, suggesting that the genetic lesion leads to a partial thymidylate deficiency. Like other viral genes controlling steps in thymidylate metabolism, the dihydrofolate reductase gene appears to be useful but not completely essential for growth.

Coliphages↗
PubMed1965

Phage Growth and Deoxyribonucleic Acid Synthesis in Escherichia coli Infected by a Thymine-Requiring Bacteriophage.

Mathews, Christopher K. (Yale University, New Haven, Conn.). Phage growth and deoxyribonucleic acid synthesis in Escherichia coli infected by a thymine-requiring bacteriophage. J. Bacteriol. 90:648-652. 1965.-Cultures of Escherichia coli B infected with a mutant strain of phage T4 which cannot induce the formation of thymidylate synthetase produce deoxyribonucleic acid (DNA) at about two-thirds the rate of cultures infected with the parent strain. Under certain conditions the yield of viable phage observed with the mutant is one-third of that brought about by the wild-type strain. Addition of thymine increases both DNA synthesis and phage production in cells infected by the mutant. It is suggested that the ability to induce thymidylate synthetase formation in infected cells confers a selective advantage on the wild-type strain.

Journal Article↗
PubMedDate not supplied

Deoxyribonucleotide pools as targets for mutagenesis by N-methyl-N-nitrosourea.

This paper describes a biological test of the hypothesis that one or more components of the intracellular nucleotide pool represent a significant target for the mutagenic effects of alkylating agents. In other words, we ask whether mutagenesis can occur either through alkylation of susceptible nucleotide residues in DNA, or through alkylation of a free nucleotide, followed by its incorporation into DNA. Our approach is based upon the premise that if a nucleotide pool is a mutagenic target, then transient expansion of that pool should increase the target size and enhance mutagenesis following subsequent treatment with an alkylating agent. Working either with V79 hamster lung fibroblasts or Chinese hamster embryo fibroblasts (CHEF/18), we treated cells for 30 min, under conditions that expanded one or more pools of deoxyribonucleoside triphosphates. This was followed immediately by a 30-min treatment with 0.5 mM N-methyl-N-nitrosourea. After 8 days of additional culture for recovery of cells and expression of mutations, we plated in selective media to determine the abundance of 6-thioguanine-resistant mutants in each culture. We found that conditions which expand pools of either dATP or dTTP and dGTP stimulate mutagenesis by MNU, with the degree of stimulation varying in different experiments from 2- to 6-fold. Although alternate interpretations can be entertained, the data are consistent with the hypothesis that nucleotide pools represent alkylation targets. A biochemical test of the hypothesis is warranted. During our studies we made several other noteworthy observations: (1) treatment of V79 cells with mutagen alone does not significantly affect dNTP pools; (2) deoxynucleotide pool perturbations are quite short-lived following transfer of cells to normal medium; (3) deoxyuridine is significantly more effective than thymidine in expanding dTTP pools; (4) deoxyuridine by itself is significantly mutagenic, particularly to CHEF/18 cells.

Animals↗