A Unique Ribonucleic Acid of Low Molecular Weight from Rat Liver Microsomes

The presence in rat liver microsomes of a unique, low molecular weight RNA is described. This RNA, which for convenience is referred to as membrane RNA, is not present in ribosomes prepared from microsomes by deoxycholate treatment. It comprises 15 to 20% of the total microsomal RNA and has the following chemical and biological properties: (a) high content of guanosine + cytidine similar to transfer RNA; (b) low content of 3'-terminal adenosine groups, methylated bases, and pseudouridylic acid; (c) heterogeneous behavior on hydroxylapatite columns; and (d) little or no amino acid acceptor activity. These properties distinguish membrane RNA from both 5 S RNA and biologically active transfer RNA. Evidence is presented which suggests that this new RNA is not the result of degradation of high molecular weight RNA during the preparative procedures used.