Complete nucleotide sequence of a mouse VL30 retro-element.

Abstract

The complete nucleotide sequence of a mouse retro-element is presented. The cloned element is composed of 4,834 base pairs (bp) with long terminal repeats of 568 bp separated by an internal region of 3,698 bp. The element did not appear to have any open reading frames that would be capable of encoding the functional proteins that are normally produced by retro-elements. However, some regions of the genome showed some homology to retroviral gag and pol open reading frames. There was no region in VL30 corresponding to a retroviral env gene. This implies that VL30 is related to retrotransposons rather than to retroviruses. The sequence also contained regions that were homologous to known reverse transcriptase priming sites and viral packaging sites. These observations, combined with the known transcriptional capacity of the VL30 promoter, suggest that VL30 relies on protein functions of other retro-elements, such as murine leukemia virus, while maintaining highly conserved cis-active promoter, packaging, and priming sites necessary for its replication and cell-to-cell transmission.The mouse VL30 elements are a family of dispersed retroviruslike DNA sequences that are present at about 200 copies per genome (24,25). A typical element is 5.0 to 6.0 kilobases (kb) in length (8, 19) with long terminal repeats (LTRs) of about 570 nucleotides (Fig. 1) that resemble the LTRs of retroviruses (4,22,33). VL30 elements fall into a broader class of murine sequences that constitutes a significant proportion of the mouse genome and includes the genomes of intracisternal A-type particles (1APs) (1,000 copies per genome) (29, 34) and the "early" transposons (300 to 500 copies per genome) (23). Structurally, these resemble eucaryotic retroviral proviruses and the retrotransposons of other eucaryotes, such as the Ty elements of yeasts (1, 16) and the copia-like elements of Drosophila spp. (31). Recent sequence information (29, 34) has shown that IAPs are most properly regarded as defective retroviruses. The status of VL30 elements is currently unknown.The major VL30 transcript is a characteristic 30S RNA which is expressed at relatively high levels and in a variety of cell types (2,7,21,26). This RNA varies between different elements but starts in the 5' LTR and terminates in the 3' LTR, so that it has a retroviruslike terminal redundancy (33). Recently, a number of VL30 LTRs were sequenced and shown to possess a typical retrovirus U3-R-U5 structure. Upstream of the RNA start site is a potential enhancer region that has homology with the murine sarcoma virus (MSV) enhancer (19) or the simian virus 40 (SV40) enhancer (33). Different LTRs have been shown to be transcriptionally active, although the efficiency varies between elements (41), possibly -reflecting differences in LTR structure. No VL30

Molecular analysis of reverse mutations from nonagouti (a) to black-and-tan (a(t)) and white-bellied agouti (Aw) reveals alternative forms of agouti transcripts.

“…1 and 2). Restriction mapping and DNA sequencing analyses of the inserted regions indicated that a and a^ each contain a complete 5.5-kb VL30 element, nearly identical to the element already reported (Adams et al 1988;Hodgson et al 1990) (Fig. 1).…”

Avian Endogenous Retrovirus EAV-HP Shares Regions of Identity with Avian Leukosis Virus Subgroup J and the Avian Retrotransposon ART-CH

“…Since the EAV-HP clones reported here are defective, the spread and multiple germ line integrations are likely to have occurred with infectious virus acting in trans as a helper virus. Such a mechanism has been suggested for the spread of other defective endogenous retroelements, including VL30 sequence in mice and the ART-CH retrotransposons in chickens (1,28). A study of the ability of the EAV-HP genomic RNA to be packaged into virus particles may provide support for this hypothesis.…”

Retroviral-mediated transmission of a mouse VL30 RNA to human melanoma cells promotes metastasis in an immunodeficient mouse model

“…A mouse VL30 retrotransposable element (mVL30 retroelement) was first identified as a 30S RNA molecule encapsulated in mouse leukemia virus (MLV) particles that were produced in a mouse packaging cell line (1)(2)(3)(4). Mouse leukemia virus and other retroviruses can transmit an encapsulated mVL30 RNA to cells infected by the retrovirus, resulting in the synthesis of VL30 cDNA mediated by retrovirus-encoded reverse transcriptase, followed by integration of the mVL30 cDNA into the cell genome (5,6).…”