Informosomal and polysomal messenger RNA. Differential kinetics of polyadenylation and nucleocytoplasmic transport in Chinese hamster ovary cells.

The relative kinetics of cytoplasmic appearance and polyadenylation were determined for informosomal (ribosome-free) and polysomal (ribosome-associated) mRNAs of cultured Chinese hamster cells. Label appeared in polysomal mRNA 17--20 min and into informosomal mRNA 2--5 min after addition of radio-labelled uridine. Adenosine appeared in polysomal mRNA 4--5 min before uridine. In contrast, adenosine label preceded uridine into informosomal mRNA by less than 1 min. About one-third of newly formed informosomal and two-thirds of newly formed polysomal mRNA are poly(A+). The data indicate that newly formed informosomal mRNA cannot be simple precursor to polysomal mRNA. Further, the pronounced difference in time required for polyadenylation and cytoplasmic appearances of these messenger ribonucleoproteins suggests that there may be fundamental differences in their mode of processing.