Livas et al. BMC Genomics 2011, 12:405 http://www.biomedcentral.com/1471-2164/12/405 Page 3 of 12 genes showed at least a 1.8-fold increase of their tran- script level and ca. 80 genes were induced by more than 4-fold. Among the genes induced by glucose, some were still strongly induced in at least one of the strains without functional TPK genes (induction factor of at least 70% of that measured in the reference strain), others were only partially induced, and still others did not show a transcriptional response to glu- cose (representative genes of each category are shown in Figure 2). For some genes, such as MIG2, the induction factor was different in the two strains lacking PKA (Figure 2). However, the observation that full induction takes place in one of the two strains was sufficient to indicate the existence of a glucose-signalling pathway independent of PKA. For genes such as HOR2, PKA may even attenuate the degree of glucose induction, which for this gene was higher in both strains lacking PKA (Figure 2). Genes encoding proteins related with glucose metabo- lism (HXT3, PFK1, ENO1, ENO2, CDC19, PDC1, ADH1, Figure 2 Consequences of the lack of PKA in the induction by glucose of some representative genes. Yeast strains TPK1 TPK2 TPK3, tpk1 tpk2 tpk3 msn2 msn4, and tpk1 tpk2 tpk3 yak1 were grown on ethanol and samples were taken before the addition of glucose to the medium and 30 min after, as described in Methods. mRNA levels were measured using Affymetrix microarrays. Biological duplicates were performed. Expression data from biological replicates generally differed from the average by less than 25%. The induction factor is the quotient of the values measured in samples incubated in the presence of glucose and in those grown in the absence of glucose. Induction is considered “total” when the induction factor is no less than 70% of that measured in the reference strain in at least one of the strains lacking PKA.