Recognition sites DNA Cut Cut Restriction enzyme cuts(magenta arrows) GAATTC GAATTC double-stranded DNA at its particular recognition sites,shown in blue. CTTAAG CTTAAG Cut cut AATTC AATTC These cuts produce a DNA G fragment with two sticky ends. G CTTAA CTTAA AATTC Sticky end CTTAA DNA from another source. perhaps a plasmid,cut with When two such fragments the same restriction enzyme of DNA cut by the same restriction enzyme come AATTC GAATTC ⊙ together,they can join CTTAAG CTTAA by base pairing. GAATIG The joined fragments will usually form either a linear TA。 The enzyme DNA ligase is molecule or a circular one, used to unite the backbones as shown here for a plasmid. of the two DNA fragments. Other combinations of GAAT producing a molecule of recombinant DNA. fragments can also occur. CTTAAG Recombinant DNA Figure 9.2Figure 9.2