Fig. 5

Models of thermoresponsive Caf1R-dependent transcriptional control of gene expression. Three models that potentially describe the Caf1R dependent thermoresponsive increase in caf1 operon transcription are shown, with their states at 25 °C and 35 °C depicted in the left and right hand side panels respectively. In model (a), the Caf1R protein is the thermoresponsive element. At 25 °C it is unable to activate transcription of the caf1 operon, regardless of its DNA binding state. At 35 °C, a conformational change allows the protein to activate transcription. Inactive Caf1R is shown as a red circle and active Caf1R as a red arc. In (b), the Caf1R protein abundance is thermoresponsive. Transcription is not thermally regulated so either Caf1R is always transcribed but only translated at 35 °C or Caf1R is stabilised at 35 °C. The increased Caf1R protein level activates transcription of the operon. In (c), the DNA is the thermoresponsive element. At 25 °C, the DNA is not in an optimal conformation for Caf1R binding, and so transcription is not activated. At 35 °C, a change in the DNA facilitates optimal Caf1R binding, and so transcription of the operon is activated. Genes are shown as coloured rectangles (red, green, yellow and blue for caf1R, caf1M, caf1A and caf1 respectively), with the Caf1R DNA binding site shown in purple. mRNA transcripts are represented as wavy lines coloured according to the gene they are transcribed from