▁en zym es ▁imp licated ▁in ▁several ▁important ▁regul atory ▁processes . ▁There ▁is ▁one ▁requirement , ▁though : ▁substr ates ▁of ▁G SK 3 ▁need ▁to ▁be ▁pre - ph osph ory l ated ▁four ▁am ino ▁ac ids ▁down stream ▁( C - termin ally ) ▁of ▁the ▁actual ▁target ▁site . ▁Thus ▁it ▁also ▁requires ▁a ▁" prim ing ▁kin ase " ▁for ▁its ▁activities . ▁In ▁the ▁case ▁of ▁beta - c aten in , ▁the ▁most ▁important ▁prim ing ▁kin ase ▁is ▁Case in ▁Kin ase ▁I ▁( CK I ). ▁Once ▁a ▁ser in - th re on ine ▁rich ▁substr ate ▁has ▁been ▁" prim ed ", ▁G SK 3 ▁can ▁" walk " ▁across ▁it ▁from ▁C - term inal ▁to ▁N - term inal ▁direction , ▁ph osph ory l ating ▁every ▁ 4 th ▁ser ine ▁or ▁thre on ine ▁resid ues ▁in ▁a ▁row . ▁This ▁process ▁will ▁result ▁in ▁dual ▁ph osph ory lation ▁of ▁the ▁a for ement ioned ▁ β - Tr CP ▁recognition ▁mot if ▁as ▁well . ▁ ▁The ▁beta - c aten in ▁destruction ▁complex ▁▁ ▁For ▁G SK 3 ▁to ▁be ▁a ▁highly ▁effective ▁kin ase ▁on ▁a ▁substr ate , ▁pre - ph osph ory lation ▁is ▁not ▁enough . ▁There ▁is ▁one ▁additional ▁requirement : ▁Similar ▁to ▁the ▁mit ogen - activ ated ▁protein ▁kin ases ▁( MA PK s ), ▁substr ates ▁need ▁to ▁associate ▁with ▁this ▁en zym e ▁through ▁high