Metabolic heterogeneity of nuclear poly (A)-containing RNA in mouse liver.

The analysis by the approach to equilibrium labeling method has shown that the poly(A)+ fraction of liver hnRNA is not a uniform class of molecules, but is comprised of two distinct subclasses with half-lives of 5 and 60 min, while the poly(A)- hnRNA was metabolically homogeneous and turned over with a rather uniform half-life of 30 min. The results suggest that (a) poly(A) synthesis and addition is not limiting for the rate of hnRNA processing, and (b) there is a correlation between the kinetics of mRNA appearance in the cytoplasm and kinetic behavior of their possible nuclear precursors.