ed ▁as ▁part ▁of ▁the ▁Type ▁III ▁secret ion ▁system ▁into ▁host ▁plant ▁cells . ▁Once ▁inside ▁the ▁host ▁cell ▁they ▁trans loc ate ▁to ▁the ▁nucle us , ▁bind ▁specific ▁DNA ▁sequences ▁within ▁host ▁prom ot ers ▁and ▁turn ▁on ▁down stream ▁gen es . ▁Every ▁part ▁of ▁this ▁process ▁is ▁thought ▁to ▁be ▁conser ved ▁across ▁all ▁T A LE s . ▁The ▁single ▁meaning ful ▁difference ▁between ▁individual ▁T A LE s , ▁based ▁on ▁current ▁understanding , ▁is ▁the ▁specific ▁DNA ▁sequence ▁that ▁each ▁T A LE ▁bind s . ▁T A LE s ▁from ▁even ▁closely ▁related ▁stra ins ▁differ ▁in ▁the ▁composition ▁of ▁repe ats ▁that ▁make ▁up ▁their ▁DNA ▁binding ▁domain . ▁Re peat ▁composition ▁determ ines ▁DNA ▁binding ▁preference . ▁In ▁particular ▁position ▁ 1 3 ▁of ▁each ▁repeat ▁conf ers ▁the ▁DNA ▁base ▁preference ▁of ▁each ▁repeat . ▁During ▁early ▁research ▁it ▁was ▁noted ▁that ▁almost ▁all ▁the ▁differences ▁between ▁repe ats ▁of ▁a ▁single ▁T A LE ▁repeat ▁array ▁are ▁found ▁in ▁positions ▁ 1 2 ▁and ▁ 1 3 ▁and ▁this ▁finding ▁led ▁to ▁the ▁hypothesis ▁that ▁these ▁resid ues ▁determine ▁base ▁preference . ▁In ▁fact ▁repeat ▁positions ▁ 1 2 ▁and ▁ 1 3 , ▁referred ▁to ▁joint ly ▁as ▁the ▁Re peat ▁Variable ▁D ires id ue ▁( R VD ) ▁are ▁commonly ▁said ▁to ▁confer ▁base ▁specific ity ▁despite ▁clear ▁evidence ▁that ▁position ▁ 1 3 ▁is ▁the ▁base ▁determ ining ▁resid ue . ▁In ▁addition ▁to ▁the ▁repeat