Role of actin and tubulin in the regulation of poly(A) polymerase-endoribonuclease IV complex from calf thymus.

The poly(A) polymerase from calf thymus (Mr = 62,000) is associated with the poly(A)-specific endoribonuclease IV (Mr = 45,000); this complex is dissociable at pH 8.2. The activities of the two enzymes in the complex are strongly inhibited by the G-actin and tubulin (both in the subunit-dissociated and in the polymeric form); F-actin was less inhibitory, while myosin and actomyosin were without any effect. Gel filtration experiments revealed a complex formation between poly(A) polymerase/endoribonuclease IV and G-actin or tubulin at an approximately 1:1 molar ratio. The homogeneous poly(A) polymerase was determined to be maximally inhibited by a 5-fold excess of G-actin and by less than a 2-fold excess of tubulin dimer, if calculated on the molecular basis. The inhibitory potency of G-actin on poly(A) polymerase was reduced after co-incubation with DNase I or phalloidin and that of tubulin by colchicine. It is suggested that actin and/or tubulin is involved also in regulation of poly(A) metabolism in intact cells.