Accumulation of giant heterogeneous RNA molecules in acute myeloid leukemia blast cells.

Time course and "chase" experiments showed that, after incubation of acute myeloid leukemia blast cells with a labeled RNA precursor, a large proportion of radioactivity remained associated with RNA molecules larger than 45 S even after several hr. Double-labeling experiments with [5-3H]uridine and [methyl-14C]methionine indicated that unmethylated giant heterogeneous RNA larger than 45 S is processed much more slowly than the 45 S ribosomal precursor, so that relatively large amounts of fairly stable RNA of the former class accumulate in the cell. The measurement of labeled giant heterogeneous RNA molecules bound to polyuridylate-fiberglass filters showed that molecules carrying polyadenylate segments seemingly turn over faster than those lacking polyadenylate.