The 7S RNA Common to Oncornaviruses and Normal Cells is Associated with Polyribosomes

Abstract

The 7S RNA species first demonstrated in avian and murine oncornaviruses and later in normal, uninfected cells is' found associated in part with cellular polyribosomes. A molar ratio of 7S RNA to 5S ribosomal RNA of 0.05 indicates that there is approximately one mole of 7S RNA per mole'of messenger RNA. Dissociation of polyribosomes with dimethylsulfoxide results in a marked decrease in the sedimentation rate of the 7 S RNA.The dimethylsiilfoxide-induced dissociation of polyribosomes and the concomitant movement of the 7S RNA from the polyribosome region into lighter regions of a sucrose gradient are both inhibited by cycloheximide, indicating that the 7S RNA is indeed associated with polyribosomes and not with a ribonucleoprotein particle sedimenting with polyribosomes.The avian oncornaviruses contain a variety of RNA components, including the 65S. genome complex (1) and discrete populations of low-molecular-weight species designated 4 S (2), 5 S (3), and 7 S (4). The virion 4S RNA is structurally (3, 5, 6) and functionally (2, 7) similar to that of the host, and the 5S RNA apparently is identical in hucleotide sequence to the host 5S ribosomal RNA (3). The function of these small RNA species remains enigmatic.The viral 7S RNA, first described from oncornaviruses by

7SL RNA, but not the 54-kd signal recognition particle protein, is an abundant component of both infectious HIV-1 and minimal virus-like particles

“…One of the first host RNAs identified in avian and murine retroviruses was a molecule with 7S sedimentation properties now known as 7SL RNA (Erikson 1969;Bishop et al 1970;Erikson et al 1973;Faras et al 1973;Sawyer and Dahlberg 1973;Walker et al 1974). The packaging of 7SL by lentiviruses has not been well studied, although one report failed to detect 7S RNA in equine infectious anemia virus (Cheevers et al 1977).…”

“…None of the tested Gag deletion derivatives separated the 7SL packaging phenotype from the ability to produce virus particles. Because 7SL encapsidation appears to be broadly conserved across a wide range of retroviral genera (this work and Bishop et al 1970;Faras et al 1973;Walker et al 1974), 7SL is not secreted by uninfected cells (Fig. 1A and not shown), and 7SL release revealed ongoing particle production even for HIV-1 derivatives that could not be assayed by RT activity or with commercially available anti-CA antibodies (Fig.…”

The Regulation of Protein Synthesis in Mammalian Cells VI. Soluble and Polyribosome Associated Components Controlling In Vitro Polypeptide Initiation in HeLa Cells

“…A 7S RNA has been found both on host polyribosomes and associated with the RNA of oncornoviruses (19).…”

Genetics of RNA Tumor Viruses

“…The 7, 5, and 4 S RNA species of RNA tumor viruses are components of the host cells, as are occasional 18 Sand 28 S ribosomal RNAs found in some virus preparations . The 7 S RNA is found in polyribosomal structures of uninfected cells (Erikson et al, 1973;Walker et al, 1974). The 5 S RNA is a part of the large subunit of normal ribosomes (Faras et al, 1973).…”