SUMMARY: The yeast 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, MgSO 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.


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