5S RNA

Abstract

INTRODUCTION
5S RNA was identified for the first time as a 50S subunit component in E. coli by Rosset and Monier (1963). It was later found in all cytoplasmic and chloroplastic ribosomes (for references see the review of Monier 1972) but not in mitochondrial ribosomes either from fungi (Lizardi and Luck 1971) or from higher organisms (Zylber and Penman 1969; Attardi et al. 1970). It remains to be seen whether a 5′-terminal section of the larger ribosomal mitochondrial RNA plays the same role as 5S RNA in other ribosomes (Lizardi and Luck 1971) or whether an RNA with a sedimentation constant of 4S replaces the usual 5S component (Wu et al. 1972).

In prokaryotes, 5S RNA is the only ribosomal RNA of low molecular weight so far identified. In eukaryotes, the larger cytoplasmic subunit also contains the so-called 7S RNA (Forget and Weissman 1967; Pene, Knight and Darnell 1968), which becomes detached from the 28S RNA after exposure to denaturing conditions. The 7S RNA in eukaryotes is part of the same transcription unit as 18S and 28S RNA (Pene, Knight and Darnell 1968), whereas 5S RNA has an entirely different genetic origin (Brown and Weber 1968). Therefore the 7S RNA, which is restricted to eukaryotic cytoplasmic ribosomes, probably has not the same significance as 5S RNA as regards the structure and function of the ribosome.

The presence in Rous sarcoma virions of a low molecular weight RNA, which has the same electrophoretic mobility and the same fingerprint as the cytoplasmic...