A nuclease acts on a 1 kb duplex substrate and breaks its ph

A nuclease acts on a 1 kb duplex substrate and breaks its phosphodiester backbone at two positions on the same strand as indicated below. Under normal lab conditions (24 degree C) what products do you expect? The 1 kb duplex remains intact Two smaller duplexes are produced Three smaller duplexes are produced A 4 bp ssDNA and a 1 kb duplex containing a 4 nt gap are produced The 1 kb duplex melts into two 1 kb ssDNA strands.

Solution

option A.

since the nuclease breaks phosphodiester bonds at the shown positions, the bonds between 2 A nucleotides and 2G nucleotides gets cleaved. However, the 4 bases GCTA remains bond to the other strand via hydrogen bonds between complementary nucleotides on the opposite strand.

therefore, the duplex remains remains intact with two nicks.

option D would seem correct, but 4 nucleotide gap would not be observed due to intact hydrogen bonds.