Polyadenylic acid-containing RNA and its polyadenylic acid sequences newly synthesized in isolated embryonic cells of Xenopus laevis.

Newly synthesized polyriboadenylic acid poly(A)]-containing RNA and its poly(A) sequences were isolated and characterized in Xenopus embryonic cells. Upon sedimentation analysis, the poly(A)-containing RNA labeled for 30 min showed a very heterogeneous size distribution ranging from 9 to >40 S. After 5 hr of labeling, the profile became much less heterogeneous and the main component was distributed in the 9–28 S region. The average molecular weight of 6.5–7.0 × 10⁵ daltons was calculated for the 5-hr labeled RNA. This poly(A)-containing RNA, comprising about 10% of the total labeled RNA, was metabolically stable and accumulated linearly for 5 hr. Gel electrophoresis of the RNA revealed the presence of little or no free poly(A) sequences. Most of the poly(A) sequences, which were isolated from 30-min labeled poly(A)-containing RNA migrated as a single discrete component approximately 150 nucleotides long. In contrast, they were slightly smaller (130 nucleotides long) and more heterogeneous, when obtained from the poly(A)-containing RNA labeled for 5 hr. From these results, it may be likely that the embryonic poly(A)-containing RNA is similar in size to the steady-state population of the poly(A)-containing RNA reported to occur in vitellogenic oocytes and cultured kidney cells of the same species.