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Developmental Pathways in Yeast

Amar J.S. Klar, Jeffrey N. Strathern, James B. Hicks


At some level, development must always rely on the proper sequence of expression of a number of genes. Corollary to this working hypothesis is the concept that coordinate control of a bank of genes may be accomplished through a common regulatory effector. This level of gene control is exemplified by the regulation of functions involved in the determination of the three different cell types observed in Saccharomyces yeasts: the two mating-proficient types known as a and α and the nonmating, sporulation-proficient type known as a/α.

Although many developmentally regulated genes have been characterized in higher eukaryotes, the means by which they are ultimately controlled are not known. It is an arduous task to trace the pathway of regulation from a cloned structural gene back to the event that initiated its tissue-specific expression. In Saccharomyces cerevisiae, however, molecular cloning coupled with genetic analysis has revealed nearly the entire pathway from the master regulatory genes to the structural genes comprising each specific cell type.

In their life cycles, Saccharomyces yeasts undergo an alternation of generation between haploid and diploid phases in a fashion similar to that in lower plants. This process involves three distinct cell types: two mating-proficient, gametic types known as a and α and the nonmating, sporulation-proficient type known as a/α. Both haploid and diploid normally grow vegetatively by mitosis and budding. Their sexual behavior is governed by the state of a single genetic locus called MAT. MAT can exist in two allelic states, MATa...

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