ABSTRACT
Poly(A) synthesizing activity has been reported in both prokaryotes and eukaryotes; the eukaryotic poly(A) polymerase is present in an array of tissues and cells such as calf thymus, sea urchin embryos, guinea-pig brain, HeLa cells, rat liver, Ehrlich ascites cells, human lymphocytes, hamster embryo fibroblast, quail oviduct, Krebs ascites cells, Landschutz ascites cells, chick chorioallantoic membrane, chick embryonic heart or liver, yeast, tobacco leaf, and corn seedlings. Poly(A) polymerase purified from almost all eukaryotic cells appears to consist of a single polypeptide with molecular weight ranging from 48,000 for rat liver nuclear enzyme to 120,000 for calf thymus nuclear enzyme. The nuclear enzyme exists as chromatin-bound and free forms, which appear to catalyze initial poly(A) addition and poly(A) extension reactions, respectively. Studies on phosphorylation of poly(A) polymerase and its effect on poly(A) synthesis have provided an important mechanism for controlling the rate of the polyadenylation reaction.
