Question

Which of the following is true for K strain for E. coli?

(a) It contains restriction-modification system which is encoded by hsDMRS locus

(b) hsDR encodes for endonuclease which is responsible for cleaving the DNA sequence containing –AACGCNNTGC-

(c) Cleavage is carried out when the second A is non methylated

(d) hsDR mutation can be used for cleavage of incoming unprotected DNA

The question was posed to me in class test.

My question comes from Transformation and Hosts topic in section Simple Cloning of Genetic Engineering

Answer 1

The correct answer is (a) It contains restriction-modification system which is encoded by hsDMRS locus

For explanation: It consists of K restriction-modification system which is encoded by hsDMRS locus. hsDR encodes for endonuclease which is responsible for cleaving the DNA sequencing containing –AACNNNNNNGTGC-. Cleavage takes place only in the case when the second A and the A opposite to T in the second strand is methylated. This mutation can be used to avoid cleavage of incoming unprotected DNA.