when pBr322 is mixed with EcoR1 why it still in the supercoiled form?

Answer 1

pBR322 does have an EcoRI site. Most likely because of an incomplete digest, where you have two forms visible on agarose gel. The supercoiled form will travel further on the gel than the linearized form (cut with EcoRI). Otherwise, your enzyme might not be active anymore. If this is the case you would see little or no linear pBR322 on a gel and mostly supercoiled. Increasing reaction time and/or adjusting template and enzyme amount could solve the problem.

Answer 2

Ecor1 Fermentas

Answer 3

If I were to guess, my guess would be that pBR322 has no EcoRI sites.