In a eukaryotic transcription assay, two transcription factors, TF3 and TF4, bind to independent cis regulatory elements (Cis3 and Cis4, respectively) upstream of the TATA box and positively regulate gene expression. A histone modifier, HM2, binds to TF3 but not to TF4. To investigate how these three factors regulate gene expression, an in vitro transcription and translation assay was performed. The experimental setup used a packaged DNA containing the region from Cis3 to Cis4, along with a minimal promoter fused upstream of a GFP (Green Fluorescent Protein) gene. The GFP fluorescence activity, upon addition of combinations of TF3, TF4, and/or HM2 in the presence of RNA polymerase and a translation mix, is plotted below.
Which of the following models best represents the result?
TF4 activates GFP expression independent of TF3 and HM2.
HM2 activates the binding of either TF3 or TF4 to their respective Cis elements to enhance GFP expression.
TF3 binds to Cis3, recruits HM2 to modify DNA, allowing TF4 to bind Cis4, leading to GFP expression.
TF4 binds to Cis4, recruits HM2 to modify DNA, facilitating the binding of TF3 to Cis3 to activate GFP expression.