The last step in glycolysis is carried out by pyruvate kinase, encoded by pkiA, converting phospho-enol-pyruvate to pyruvate for metabolism to oxaloacetate and acetyl-CoA. The key step in gluconeogenesis is conversion of oxaloacetate to phospho-enol-pyruvate by PEP carboxykinase, encoded by acuF. Simultaneous activity of these enzymes would generate a nasty futile cycle. A number of observations suggests that control of the expression of these two genes involves activation of sense transcription and negative control by activation of antisense transcription. For pkiA, ChIP studies have found binding of the gluconeogenic activators AcuK and AcuM and of the acetate dependent FacB activator in the downstream region. Cognate binding sites are conserved in filamentous ascomycetes. RNA Seq, polII ChIP and RT-PCR analysis indicates antisense transcription during growth on acetate or proline as carbon sources. Old data (de Graaf, van den Broek, Visser; Cur. Genetics 13: 315, 1988) showed that transformation of a construct lacking these 3’ sites resulted in inappropriate pkiA expression on acetate. In response to growth on gluconeogenic carbon sources, the acuF gene is activated by AcuK and AcuM binding to sites in the 5’ upstream region. Studies with an acuF-lacZ gene fusion indicate positive control by AcuK and AcuM but a loss of the glucose repression observed in Northerns suggesting negative regulation acting via 3’ sequences in response to growth on glycolytic carbon sources. Support for this is provided by transcription studies. Modulation of the balance between the opposing activities of these two gene products is proposed to result from transcriptional interference involving collision of RNA polymerase molecules.
Full conference title:
27th Fungal Genetics Conference
- Fungal Genetics Conference 27th (2013)