Addition of glucose to yeast cells growing on less preferred carbon sources triggers profound changes in the expression levels of several genes. This paper focuses on the signal transduction pathways leading to transcriptional activation of the glycolysis in Saccharomyces cerevisiae during the transition from respiratory to fermentative growth conditions. To this end, we studied the transcriptional regulation of glycolytic genes (PFK1, PYK1 and PDC), one gluconeogenic gene (FBP1) and the two genes encoding the 6-phosphofructo-2-kinase isoenzymes (PFK26 and PFK27) during this transition. The results of experiments using glycolysis mutants, different fermentable carbon sources and 2-deoxyglucose indicate that proper transcriptional regulation of these genes is dependent on the ability to form glucose 6-phosphate by any one of the three hexose kinases. In addition, we conclude that signalling via the Ras-adenylate cyclase pathway is not necessary for the proper transcriptional response of glycolytic and gluconeogenic genes to glucose, because the transcription of these genes is not significantly affected in mutants having either high or low activities of this pathway. In contrast, the transcriptional regulation of the PFK26 and PFK27 genes is significantly altered in several of the Ras-adenylate cyclase pathway mutants studied, indicating that protein kinase A plays an important role in the transcriptional regulation of these genes.