Comparison of Cytoplasmic and Nuclear Poly(A)‐Containing RNA Sequences in Xenopus Liver Cells

Abstract

Poly(A)-containing RNAs from cytoplasm and nuclei of adult Xenopus liver cells are compared. After denaturation of the RNA by dimethylsulfoxide the average molecule of nuclear poly(A)-containing RNA has a sedimentation value of 28 S whereas the cytoplasmic poly(A)-containing RNA sediments slightly ahead of 18 S. To compare the complexity of cytoplasmic and nuclear poly(A)-containing RNA, complementary DNA (cDNA) transcribed on either cytoplasmic or nuclear RNA is hybridized to the RNA used as a template. The hybridization kinetics suggest a higher complexity of the nuclear RNA compared to the cytoplasmic fraction. Direct evidence of a higher complexity of nuclear poly(A)-containing RNA is shown by the fact that 30% of the nuclear cDNA fails to hybridize with cytoplasmic poly(A)-containing RNA. An attempt to isolate a specific probe for this nucleus-restricted poly(A)-containing RNA reveals that more than 104 different nuclear RNA sequences adjacent to the poly(A) do not get into the cytoplasm. A poly(A) on a nuclear RNA probably does not ensure the transport of the adjacent sequence to the cytoplasm.