DIVISION SYNCHRONIZATION IN A RESPIRATORY DEFICIENT YEAST'

Synchronization of cell division in a variety of microorganisms has been achieved by tempera-ture shifts or by starvation. Two reports exist which mention svnchronization of the budding process in yeast by starvation (Beam et al., 1954; Ogur et al., 1953). In both cases, the demon-stration of synchronization was incidental to the primary purpose of the experiments performed, and was therefore not quite so complete as one might like. In the present study, starvation was for glu-cose. Starvation for glucose alone on a complete medium was achieved by the use of a respiratory deficient strain which will grow on yeast extract and peptone only with the addition of a fer-mentable substrate. It was felt that, just as periodic temperature shifts have been useful in some synchronization procedures (Lark and Maaloe, 1954; Zeuthen and Scherbaum, 1954), that periodic starvation might likewise enhance the degree of synchronization. It will be seen that this expectation was not confirmed. MATERIALS AND METHODS The yeast strain 19.1, a haploid segregant from the Winge strain 55 (Saccharomyces chevalieri X S. cerevisiae hybrid) has been described previ-ously (Campbell and Spiegelman, 1956.) The yeast extract peptone medium was made by adding the following to 1 L of water: (NH4)2SO4, 6 g; KH2PO4, 2 g; CaCl2 2H20, 0.25 g; MgSO4* 7H20, 0.25 g; 60 per cent sodium lactate, 6 ml; agar (where added), 20 g; carbohydrate as specified. Synthetic medium was made according to the formula of Burkholder (1943). Direct microscopic counts of cell suspensions were generally made in a Spencer bright line counting chamber and occasionally in a Petroff Hauser chamber. Cells were classified by visua