ers ▁each ▁begin ▁to ▁rec ruit ▁an ▁Ar p 2 / 3 ▁complex ▁to ▁F - act in . ▁It ▁bind s ▁to ▁Ar p 2 / 3 ▁with ▁an ▁as part ic ▁acid - as part ic ▁acid - try pt oph an ▁( DD W ) ▁sequence ▁in ▁its ▁N TA ▁region , ▁a ▁mot if ▁that ▁is ▁often ▁seen ▁in ▁other ▁act in ▁nucle ation - prom oting ▁factors ▁( N PF s ). ▁ ▁C ertain ▁ser ine / th re on ine ▁kin ases , ▁such ▁as ▁ER K , ▁can ▁ph osph ory late ▁cort act in ▁on ▁Ser 4 0 5 ▁and ▁Ser 4 1 8 ▁in ▁the ▁SH 3 ▁domain . ▁Activ ated ▁like ▁this , ▁it ▁still ▁associ ates ▁with ▁Ar p 2 / 3 ▁and ▁F - act in , ▁but ▁will ▁also ▁allow ▁other ▁act in ▁N PF s , ▁most ▁important ly ▁N - W AS p ▁( N eur onal ▁W isk ott - A ld rich ▁synd rome ▁protein ), ▁to ▁bind ▁to ▁the ▁complex ▁as ▁well ; ▁when ▁ph osph ory l ated ▁by ▁ty ros ine ▁kin ases , ▁other ▁N PF s ▁are ▁ex cluded . ▁The ▁ability ▁of ▁these ▁other ▁N PF s ▁to ▁bind ▁the ▁Ar p 2 / 3 ▁complex ▁while ▁cort act in ▁is ▁also ▁bound ▁could ▁come ▁from ▁new ▁interactions ▁with ▁cort act in ' s ▁SH 3 ▁domain , ▁which ▁is ▁in ▁a ▁different ▁con formation ▁when ▁ph osph ory