Which of the Following Statements About E

Question

Which of the following statements about E. coli DNA polymerase I is FALSE?
A) It can copy a circular DNA template but cannot join the ends.
B) It can extend a gapped duplex from a 3'OH group and displace a preexisting 5' end.
C) The 3' exonuclease site is some distance from the polymerase active site.
D) It has 3' exonuclease activity that resides in a small N-terminal fragment that can be cleaved off by limited proteolysis.
E) It has 5' exonuclease activity that resides in a small N-terminal fragment that can be cleaved off by limited proteolysis.

Accepted Answer

E. coli DNA polymerase I's 3' exonuclease activity, which is responsible for proofreading, is not located in a small N-terminal fragment. Instead, it is the 5' exonuclease activity that can be removed by cleaving a small N-terminal fragment, leaving behind the Klenow fragment with polymerase and 3' to 5' exonuclease activity.