Conformational change of DNA binding subunit of RNA polymerase II on binding to DNA.

The spatial arrangement of the subunits of RNA polymerase II from Ehrlich ascites tumor cells was investigated by measuring the sensitivity of each subunit in the native enzyme to various proteinases. The results showed that the largest two subunits (a and b) were sensitive to all the proteinases tested, whereas two smaller subunits (e and h) were resistant to these enzymes. These results suggest that in the native enzyme subunits e and h are located in the inside of RNA polymerase II, forming a core. It was also found that the conformation of the DNA binding subunit a changes when the enzyme binds to DNA, and it becomes much more susceptible to chymotryptic digestion.