Effect of tryptophan on rat hepatic nuclear poly(A)polymerase activity

Addition of poly(A) to hnRNA in the cell nucleus is a post-transcriptional event and is presumed to be brought about by a specific poly(A)polymerase. Since it is known that tryptophan rapidly increases the cytoplasmic levels of polyadenylated mRNA, it was of interest to investigate whether the essential amino acid, tryptophan, affects the enzyme responsible for polyadenylation. Tryptophan (300 mg/kg body wt.) tube-fed for 10 min elevated the hepatic nuclear enzymatic activities of both the chromatin-bound nuclear poly(A)polymerase (44%, n = 7) as well as that of the free solubilized form (48%, n = 7). Hepatic nuclear proteins separated under denaturing conditions, transferred to nitrocellulose sheets, and then probed with antibody raised against hepatic nuclear poly(A)polymerase showed no differences between the hepatic nuclei of control and tryptophan-treated rats.