Normal synthesis, transport and decay of mRNA in the absence of its translation

Abstract

MESSENGER RNA (mRNA) in the cytoplasm of eukaryotic cells constitutes a small fraction of the total RNA synthesised in the nucleus¹. This mRNA seems to be selected from the heterogeneous nuclear RNA (hnRNA) and transported to the cytoplasm where it decays much less rapidly than the hnRNA, which decays in the nucleus. In sea urchin embryos about 10% of the total RNA synthesised in the nucleus becomes cytoplasmic mRNA which decays 10 times less rapidly than the hnRNA. In L cells 2% of the RNA is transported and it decays 50 times less rapidly than hnRNA³. Several proposed models implicate ribosomes or ribosomal subunits in mRNA transport or decay^4–6, and we have tested these possibilities in sea urchin embryos using pactamycin to inhibit the association of ribosomes with mRNA⁷ and precursor pool techniques worked out in this laboratory for measuring RNA metabolism². The results show that neither synthesis, transport nor decay of mRNA depend on or are regulated by concurrent protein synthesis.