Selection of ZFRs to recombine casein gene sequences.

<p>(<b>A</b>) Activity of the progenitor ZFR (ZFR300) on Z-sites with central sequences from Tn<i>3 res</i> site I or the casein gene intron 1. The substrate plasmids each contained two identical Z-sites as indicated above the gel lanes. The numbers below each lane represent the percentage of recombinant plasmids in the recovered DNA (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019537#s2" target="_blank">Materials and Methods</a>). Images of the ethidium-stained gels are greyscale-inverted, and a uniform background subtraction has been applied. A representative sector of a plate from the corresponding MacConkey-galactose assay is shown above each lane. Annotation: exp, ZFR expression plasmid; nr, non-recombinant substrate plasmid; rec, recombinant (<i>galK</i>⁻) plasmid. (<b>B</b>) Activity of the first round mutant I77L (ZFR310) on the same substrates as in <b>A</b>. (<b>C</b>) Activity of the second round double mutant I77L E132A (ZFR320) on the same substrates as in <b>A</b>.