Step I (Enzyme A): Eco RI Function: It is a specific restriction endonuclease. Mechanism: It recognizes the palindromic sequence 5'-GAATTC-3' on both the vector DNA and the foreign DNA. It cuts both strands between the G and A bases, leaving overhanging single-stranded stretches called sticky ends (AATT).

Step II (Enzyme B): DNA ligase Function: It is a molecular glue or joining enzyme. Mechanism: It seals the nicks between the complementary sticky ends of the vector DNA and foreign DNA by forming phosphodiester bonds, resulting in Recombinant DNA.