Synthesis of poly(a) polymerase from conserved messenger RNA in germinating excised embryos of wheat

Abstract

A 3.5–6.0-fold stimulation of poly(A) polymerase activity was observed in excised wheat embryos germinated for 48 hr. Addition of primer RNA to the enzyme assay mixture was necessary for the incorporation of [ 3H]AMP into the acid-precipitable polyadenylate product. Administration of six amino acid analogues (1 mM each) or cycloheximide (10 μg/ml) to the germinating embryos resulted in 77–82 % inhibition of poly(A) polymerase activity. The inhibitory response, elicited by the analogues, was substantially counteracted by the simultaneous addition of the corresponding six amino acids (2 mM each). This indicated that de novo protein synthesis was necessary for the enhancement of poly(A) polymerase activity. Cordycepin, a potent inhibitor of transcription, failed to block poly(A) polymerase activity; instead, the drug invariably brought about a significant stimulation ( ca 1.7–4.0-fold of the enzyme activity. Cordycepin, however, inhibited acid phosphatase activity by 77% in germinating wheat embryos. Actinomycin D also failed to inhibit poly(A) polymerase activity in germinating wheat embryos. The lack of inhibition of poly(A) polymerase by transcriptional inhibitors during early germination suggested that the enzyme was translated from its conserved mRNA, already stored in the dry wheat embryos.