Abstract
A method for identifying yeast genes whose transcription is differentially regulated was developed. The technique is based on incorporation of the analog 4-thiouridine into nascent RNAs, which allows their purification. The purified RNAs are used to prepare cDNA copies for screening of genomic DNA libraries by hybridization. Using this procedure, several cloned yeast DNA segments were found whose transcription in MATa haploids in vivo is apparently modulated in dramatic fashion within 10-15 min after exposure to the mating pheromone, alpha factor. Subsequent analysis indicated that these sequences fall into three major classes: (i) genes expressed in vegetatively growing cells that are no longer transcribed after alpha-factor administration ("turn-off" genes); (ii) genes whose expression is increased 10- to 20-fold after exposure of the MATa cells to alpha factor ("turn-up" genes); and (iii) genes that are expressed only after alpha-factor treatment ("turn-on" genes). The first class may encode products required for cell cycle progression; the third class may code for products uniquely involved in the mating process.