Does transcription factors interacted more than the overall PPI?

Question

[pengchy]

Hi,

There are many genome wide protein-protein interaction database, like HPRD and iRefIndex. However, I haven't found paper focus on the interactions among the transcription factors genome widely, or comparing with the genome wide PPI overall. I want to know whether transcription factors interact more than the background overall PPI.

I think this work should be done and a paper there, but I can not found it after searching. Does anyone know?

Thank you!

Best,