A study of minor RNA components of rat-liver microsomes

Abstract

1. 1. RNA preparations isolated under various conditions from rat liver or rat-liver microsomes always contained small amounts of distinct RNA components migrating through polyacrylamide gels between the two major ribosomal RNAs. The apparent molecular weights of three well-separated minor components were 1.4 · 10 6, 1.3 · 10 6 and 1.05 · 10 6; in addition three poorly separated bands migrated with apparent molecular weights between 0.95 · 10 6 and 0.85 · 10 6. 2. 2. Incubation of a post-mitochondrial supernatant in buffered 0.23 M sucrose containing 1 mM EDTA, led to a gradual disappearance of 28-S ribosomal RNA with a concomitant increase of some of the minor components. No preferential formation of these components was observed when the incubation was carried out in the presence of 5 mM MgCl 2 or MgCl 2 plus 1.3 % deoxycholate. 3. 3. When RNA components were isolated from rats that had received [ 3H]orotate and 32P, 3 weeks and 24 h, respectively, before killing, the 3 H 32 P ratio was much higher in the minor components than in the main ribosomal RNAs or in the heterogeneous RNA migrating slower than 28-S RNA. 4. 4. We conclude that the minor components represent intermediates in the degradation of ribosomal RNA in vivo.