- long ▁segments ▁that ▁are ▁highly ▁conser ved ▁among ▁cort act in ▁prote ins ▁of ▁all ▁species ▁and ▁repeated ▁up ▁to ▁ 6 . 5 ▁times ▁in ▁tan dem ▁( “ c ort act in ▁repe ats ” ); ▁a ▁pro line - rich ▁region ; ▁and ▁an ▁SH 3 ▁domain . ▁This ▁basic ▁structure ▁is ▁highly ▁conser ved ▁among ▁all ▁species ▁that ▁express ▁cort act in . ▁ ▁Activ ation ▁and ▁binding ▁▁ ▁Cort act in ▁is ▁activ ated ▁via ▁ph osph ory lation , ▁by ▁ty ros ine ▁kin ases ▁or ▁ser ine / th re on ine ▁kin ases , ▁in ▁response ▁to ▁ext rac ell ular ▁signals ▁like ▁growth ▁factors , ▁ad hes ion ▁sites , ▁or ▁path ogen ic ▁invasion ▁of ▁the ▁ep ith el ial ▁layer . ▁ ▁The ▁SH 3 ▁domain ▁of ▁certain ▁ty ros ine ▁kin ases , ▁such ▁as ▁the ▁on c ogene ▁S rc ▁kin ase , ▁bind s ▁to ▁cort act in ' s ▁pro line - rich ▁region ▁and ▁ph osph ory l ates ▁it ▁on ▁T yr 4 2 1 , ▁T yr 4 6 6 , ▁and ▁T yr 4 8 2 . ▁Once ▁activ ated ▁in ▁this ▁way , ▁it ▁can ▁bind ▁to ▁fil ament ous ▁act in ▁( F - act in ) ▁with ▁the ▁fourth ▁of ▁its ▁cort act in ▁repe ats . ▁As ▁the ▁concentration ▁of ▁ph osph ory l ated ▁cort act in ▁increases ▁in ▁specific ▁regions ▁within ▁the ▁cell , ▁the ▁mon om