| The regulator of G protein signaling , RGS 4 , interacted with the COPI subunit beta ' COP in a yeast two hybrid screen . ^^^ Both recombinant RGS 4 and RGS 2 bound purified recombinant beta ' COP in vitro . ^^^ Binding of beta ' COP to RGS 4 occurred through two dilysine motifs in RGS 4 , similar to those contained in some aminoglycoside antibiotics that are known to bind coatomer . ^^^ |