Component of the multisynthase complex which is comprised of a bifunctional glutamylprolyltRNA synthase, the monospecific isoleucyl, leucyl, glutaminyl, methionyl, lysyl, arginyl and aspartyl-tRNA synthases, and three auxiliary proteins, EEF1E1/p18, AIMP2/p38 and AIMP1/p43. p18 is a cofactor of multi-ARS complex and regulates p53 through the interaction with ATM/ATR.