Poly (A) Polymerase and Poly (G) Polymerase in Wheat Chloroplasts

Extracts of wheat chloroplasts contain a poly(A) polymerase which can polymerize AMP residues from ATP onto an RNA primer. Whole extracts of wheat leaves also contain another poly(A) polymerase which is present in much larger amount and is probably derived from the nuclei. Both polymerases can utilize as primer poly(A), poly(C), transfer RNA, and ribosomal RNA, but only the chloroplast polymerase can utilize poly(U) and poly(G). Both enzymes have a specific requirement for ATP. Extracts of wheat chloroplasts contain, in addition to the poly(A) polymerase, a poly(G) polymerase which can polymerize GMP residues from GTP onto primers such as poly(G), poly(A), or ribosomal RNA. The poly(G) polymerase cannot utilize ATP but can slowly polymerize CMP from CTP. When the two chloroplast polymerases are present together in an in vitro incubation with ATP plus GTP and poly(A), the polymerization product is a mixed poly(A,G) tract.