Delayed processing/export of messenger RNA under conditions of reduced protein synthesis.

The rates of processing and export of a variety of nuclear RNA species into the cytoplasmic compartment were studied by determining the rates of incorporation of tritiated uridine into nuclear and cytoplasmic RNA species. In exponentially growing cells, the rates of nuclear processing/export varied by more than a factor of ten for the six different mRNA species that were examined. Differences in the rates did not appear to be correlated with either the number or the sizes of introns in the genes for the RNA species. When cells were maintained under conditions of reduced protein synthesis (starvation for isoleucine and glutamine or exposure to cycloheximide), the processing rates for each species decreased by a factor of about 3. The decrease was not caused by the inability of hnRNA to associate with proteins, since the nuclear RNP distribution appeared normal in amino acid-starved cells.