Showing papers by "Thomas D. Brock published in 1961"

Physiology of the conjugation process in the yeast Hansenula wingei.

Abstract: SUMMARY: The yeast Hansenula wingei is a favourable organism for study of the physiology of the conjugation process (cell fusion). Microscopic observations on fusion are presented which reveal that the mating cells in contact fuse by a softening of the cell wall, followed by formation of a conjugation tube, dissolution of the cross-walls between them, and formation of a new bud at the point of juncture of the two cells. A simple technique for studying fusion in a liquid medium is described. Up to 80% of the cells will fuse in 5 hr. at 30† in a medium containing an energy source, MgSO4 and potassium phosphate, under conditions in which no growth or budding of unmated cells would occur. Synthesis of new protein is required for fusion as shown by inhibition by amino acid analogues. The precursors for this new protein come from the amino acid pool. Both mating types must be able to function for conjugation to occur. It is postulated that each mating type produces an inducer which diffuses into the opposite type. Each inducer brings about the synthesis of a wall-softening enzyme which acts upon the cell producing it. Cell fusion is viewed as an extension of the normal budding process.

Reversal of azaserine by phenylalanine.

Abstract: Kaplan, Reilly, and Stock (1959) have studied the reversal of azaserine by aromatic amino acids and have hypothesized without any direct evidence that these substances prevent the binding or penetration of the antibiotic into the cell. The present paper presents more direct evidence that this hypothesis is correct. It is shown that azaserine acts on nongrowing cells of Escherichia coli strain ML35 in such a way that subsequent growth in azaserine-free medium leads to increases in permeability, lysis, and death. It has been found that phenylalanine reverses only when it is present during the azaserine treatment and has no effect when present during the subsequent growth period. These results are interpreted to mean that phenylalanine prevents the binding or penetration of azaserine into the cell, but plays no direct role in preventing the metabolic disarrangements caused by azaserine. This work has been aided by a strain (ML35) of E. coli which forms 0-galactosidase constitutively at high levels but lacks a permease. This strain is useful in detecting nonspecific effects on permeability.

RNA synthesis and degradation during antibiotic treatment and its relation to antibiotic-induced lag.

Abstract: SUMMARY: When growing cells of Escherichia coli were treated with chloramphenicol or erythromycin for 1 hr. and then suspended in antibiotic-free medium, there was a 45 min. lag before growth resumed. By eliminating growth factors or other essential nutrients during antibiotic treatment, it was possible to show that the lag occurred only when ribonucleic acid (RNA) synthesis could take place and did not require the synthesis of deoxyribonucleic acid (DNA). This antibiotic-induced RNA was apparently abnormal and was degraded when the antibiotic was removed. This degradation is a hydrolytic process and does not require the presence of a complete growth medium. During the recovery from the antibiotic-induced lag, DNA and protein synthesis did not occur, but RNA synthesis occurred, even though this new RNA synthesis was not required for the lag to be overcome. When antibiotic-treated cells were suspended in phosphate buffer, a decrease in optical density of the suspension occurred which resembled a lytic process, but lysis apparently did not occur. Although these results clarify considerably earlier observations on antibiotic-induced lag, they leave unsolved the question of why the antibiotic-induced RNA is abnormal, and how it brings about the lag.