Regulation of Transcription in Yeast

Abstract

Studies on synchronous cultures of yeast have provided a large body of information in favor of periodic synthesis. This has been extensively reviewed in recent years (Donachie and Masters, 1969; Halvorson et al., 1971; Mitchison, 1971; Hartwell et al, 1974). Over 30–40 enzymes have been followed throughout the cell cycle in yeast. The vast majority of these show periodic synthesis restricted to some part of the cell cycle, whereas a few apparently show continuous synthesis through the cell cycle. There is no clear association of the period of enzyme synthesis with the S period. The period of synthesis is, however, spread over the cell cycle. Two major theories have been proposed to explain the control of synthesis of yeast enzymes. The “oscillatory repression” model has been proposed by several groups (Donachie and Masters, 1969; Pardee, 1966; Masters and Donachie, 1966; Goodwin, 1966) which assumes that biosynthetic enzymes are controlled by end-product repression. Given appropriate constants, a negative feed-back system will oscillate. The supporters of this hypothesis have argued that the oscillations are entrained by a cell cycle dependent event. This theory fits much of the data in synchronous bacterial cultures (Donachie and Masters, 1969; Halvorson et al, 1971; Mitchison, 1971) and some cases in eukaryotic cells such as the ribulose 1,5-diphosphate carboxylase in Chlorella (Malloy and Schmidt, 1970). However, oscillatory repression does not fit several enzymes in yeast. Ornithine transcarbamylase is a step enzyme in fission yeast, however, Stebbing (1972) found no fluctuations in the amino acid pools during the cell cycle of either repressed of constitutive synthesis.

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