SEPARATION AND CHARACTERIZATION OF LOW-MOLECULAR-WEIGHT NUCLEAR-RNA SPECIES THAT INHIBIT CELL-FREE PROTEIN-SYNTHESIS

Various RNA fractions were isolated from nuclei of 12 day lactating rat mammary glands and examined for their ability to inhibit cell-free protein synthesis. Although total nuclear RNA was generally inactive, material contained in the poly(A)+ nuclear RNA fraction and the low-MW RNA derived from total nuclear RNA by sucrose gradient centrifugation, inhibited the translation of several mRNA but not poly(U) or poly(A). Separation of the small nuclear RNA by preparative polyacrylamide-urea gel electrophoresis allowed the identification of at least 3 active inhibitor RNA species. These differed with respect to their ability to inhibit protein synthesis and in their mechanism of action. While 2 of the RNA species inhibited elongation the other inhibited initiation of protein synthesis.