The newly replicated daughter strand (red) contains a T mismatched to G in the template strand (blue). The repaired strand is shown in black. The mismatch repair system identifies the daughter strand because it is not yet methylated. Thus, this system must function before the newly replicated daughter strand becomes methylated, through action of the Dam methylase on the A residue in the GATC sequence. In a reaction dependent on ATP hydrolysis, complexes between a MutS dimer and a DNA heteroduplex are converted to protein-stabilized, alpha-shaped loop structures with the mismatch in most cases located within the DNA loop. Loop formation depends on ATP hydrolysis. The rate of MutS-mediated DNA loop growth is enhanced by MutL, and when both proteins are present, both are found at the base of alpha-loop structures. Note: the figure in the textbook has several errors. First, the cleavage by mutH is shown incorrectly: the cleavage is just 5' to the GATC sequence in the unmethylated strand. The cleavage has been corrected in this figure. Second, the polarity of the strands in the textbook figure is not correct. The polarity of the strands is correct in this figure.