Cleavage

Cleavage

Cleavage
Restriction enzymes recognize and cleave at specific sites on DNA most of these sequences are tetranucleotide Or hexanucleotide pairs which show a characteristic two fold rotational symmetry (palindromic sequences).

The Eco RII site is unique in that it contains an odd number (5) of base pairs, with the axis of symmetry passing through the central A:T pair : CCTGG CCACC

Two types of 5' termini are thus formed, and, therefore, all fragment ends are not necessarily mutually cohesive.Sometimes enzymes from unrelated Organisms can recognize the same nucleotide sequences.

For example, restriction enzymes with GGCC specificity have been found in Bacillus, subtilis, Haemophilus egyptius and Haemophilus haemoglobinophilus. Such enzymes are called isoschizomers

Cleavage positions may be either 'even' (e. g. Hind II) or 'staggered'(e. g. EcoRI). In even cleavage the breaks on the two strands are exactly opposite each other. Such breaks do not produce unpaired terminal nucleotides. Staggered breaks are separated by several nucleotides and produce complementary single stranded sticky ends.

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