EcoRI is used to cut:

The correct answer is Option (1) → DNA between bases G and A only when sequence GAATTC is present in DNA.

EcoRI is a restriction endonuclease. It recognises one specific palindromic sequence of six base pairs. In a palindrome the base sequence reads the same in the 5′→3′ direction on both strands: 5′-GAATTC-3′ on one strand and 3′-CTTAAG-5′ on the other.

(1) DNA between bases G and A only when sequence GAATTC is present in DNA. — Correct. EcoRI cuts each strand between G and A, a little away from the centre of the site. This leaves single-stranded “sticky” ends that can pair with a matching end.

(2) DNA between bases G and T only when sequence GTAATTC is present in DNA. — Incorrect. GTAATTC is not the EcoRI site. It has seven bases, and it is not a palindrome.

(3) DNA between bases A and A only when sequence GTAATTC is present in DNA. — Incorrect. The recognition site is wrong, and EcoRI does not cut between two A bases.

(4) DNA between bases T and T only when sequence GTAATTC is present in DNA. — Incorrect. The recognition site is wrong, and EcoRI does not cut between two T bases.