The Septation Initiation Network (SIN) is a conserved signal transduction network, which is important for cytokinesis in S. pombe. The SIN component Etd1p is required for association of some SIN proteins with the spindle pole body (SPB) during anaphase and for contractile ring formation. We show that tethering of Cdc7p or Sid1p to the SIN scaffold Cdc11p at the SPB, rescues etd1-. Analysis of a suppressor of the mutant etd1-M9 revealed that SIN signalling is influenced by the cell’s carbon source. Growth on the non-fermentable carbon source glycerol reduces the requirement for SIN signalling, but does not bypass it. The decreased need for SIN signalling is mediated largely by reduction of protein kinase A activity, and it is phenocopied by deletion of pka1 on glucose medium. We conclude that protein kinase A is an important regulator of the SIN and that SIN signalling is regulated by the cell’s carbon source.