Eukaryotic transcription factors TF1 and TF2 bind to independent cis regulatory elements (Cis1 and Cis2, respectively) upstream of TATA box and positively regulate gene expression. Histone modifier 1 (HM1) binds to TF1 but not to TF2. In order to determine how genes are regulated by these three factors, an in vitro transcription and translation assay was set up. A packaged DNA containing region from Cis1 to Cis2, along with eukaryotic minimal promoter fused upstream of a luciferase gene, was purified. The luciferase activity, upon addition of a combination of TF1, TF2 and/or HM1, in presence of RNA polymerase and translation mix is plotted below.
Which one of the following models best represents the results above?
1
TF2 activates luciferase expression independent of TF1 and HM1.
2
HM1 activates binding of either of TF1 or TF2 to their cognate Cis elements to activate luciferase expression.
3
TF1 binds to Cis1, recruits HM1 to modify DNA allowing TF2 to bind Cis2 to enhance luciferase expression.
4
TF2 binds to Cis2, recruits HM1 to modify DNA allowing TF1 to bind Cis1 to activate luciferase expression.