Changing patterns of gene expression during sporulation in yeast.

Analysis of RNAs isolated from the yeast Saccharomyces cerevisiae reveals a dramatic series of changes in protein coding sequences during sporulation. Shortly after transfer to sporulation medium, mRNAs for certain proteins are repressed while a broad array of mRNAs for other proteins is induced. Superimposed on this general increase in transcriptional activity is the very strong induction of a particular subset of heat shock mRNAs, the same subset that is induced during the normal course of oogenesis in Drosophila. At distinct times later in sporulation, two sets of abundant mRNAs are coordinately induced. Unlike the earlier changes in the message complement, these changes are unique to sporulating cells. As asci mature, one set of sporulation-specific RNAs is selectively degraded. The second set, as well as the broad array of mRNAs induced earlier in development, is retained in a highly stable and fully translatable form.