Modern - Blog Science Connections
Modern - Blog Science Connections
Modern - Blog Science Connections
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that in addition to the LTR, MSV sequences<br />
immediatly preceeding V-mos are required for<br />
transformation (McClements et al. 1980).<br />
However, the data do not rule out the possibility<br />
that the mere removal of these cellular<br />
sequences allows transformation by C-mos.<br />
There may be controlling cellular sequences<br />
preceeding C-mos that block its expression.<br />
The activation of C-mos in clone pTS 1 is<br />
consistent with this interpretation if (1) the<br />
LTR sequences override the cellular control<br />
elements or (2) the putative controlling cellular<br />
sequences are more than approximately<br />
600 bp before C-mos. The latter possibility<br />
suggests that removing normal cell sequences<br />
5' to C-mos should activate its malignant<br />
potential in the transfection assay. Indeed, this<br />
is consistent with the model proposed by<br />
Cooper et al. (1980) to explain the transforming<br />
activity of normal cellular DNA after<br />
shearing.<br />
Because the LTR is directly repeated at both<br />
ends of the provirus it could be expected to<br />
allow transcription to occur from the 3' LTR<br />
into the cell genome. Thus, random integration<br />
of retroviruses into multiple sites in the host<br />
cell genome (see Weinberg 1980 for review)<br />
could result in the activation of normally<br />
quiescent cell genes. For example, 17 out of 19<br />
tumors isolated from birds infected with avian<br />
leukosis virus show evidence for activation of<br />
expression of normal cell sequences by LTR<br />
sequerices (Hayward et al. this volume). The<br />
loss of almost all of the retrovirus genome in<br />
so me of the tumors, except for a residual LTR,<br />
could mean that LTR-promoted expression of<br />
normal cell sequences is responsible for the<br />
disease. Certainly in this case all other avian<br />
leukosis viral genes can be excluded. We have<br />
shown with pTS 1 (Table 3) that a single LTR<br />
which is linked 5' to C-mos activates transformation.<br />
This in vitro construction is analogous<br />
to a retrovirus integrating 5' (upstream) to<br />
anormal cell sequence (e.g., C-mos) in vivo,<br />
whereby the 3' LTR could activate expression<br />
of this sequence and cause transformation.<br />
This may be a useful model for other (nonviral)<br />
forms of transformation. Normal cellular<br />
sequences with functional properties of an<br />
LTR (e.g., an eukaryotic IS element) could become<br />
juxtaposed to quiescent cellular genes<br />
with transformation potential as a result<br />
of either chemically induced, radiation induced,<br />
or simply spontaneous genomic arrangements.<br />
References<br />
Aaronson S, Canaani E, Robbins K, Andersson P,<br />
Tronick S (to be published) Cellular origin of the<br />
transforming gene of Moloney murine sareoma<br />
virus. Cold Spring Harbor Symp Quant Biol 44<br />
- Andersson P, Goldfarb MP, Weinberg (1979)<br />
A defined subgenomie fragment of in vitro synthesized<br />
Moloney sareoma virus DNA ean induee eell<br />
transformation upon transfeetion. Cell 16: 63-75<br />
- Blair DG, MeClements W, Oskarrson M, Fisehinger<br />
P, Vande Woude GF (1980) The biological<br />
aetivity of c10ned Moloney sareoma virus DNA:<br />
terminally redundant sequenees may enhanee transformation<br />
efficieney. Proe Natl Aead Sei USA<br />
77 :3504-3508-BukhariAI, ShapiroJA,AdhyaSL<br />
(eds) (1977) DNA insertion elements, plasmids and<br />
episomes. Cold Spring Harbor Laboratory, New<br />
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(1979) The transforming gene of Moloney murine<br />
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Okenquist S, Silverman L (1980) Transforming<br />
aetivity of DNA of ehemically transformed and<br />
normal eells. Nature 284:418-421 - Dhar R,<br />
MeClements W, Enquist LW, Vande Woude GF<br />
Nuc1eotide sequenees of integrated Moloney sareoma<br />
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A new teehnique for the assay of infeetivity of human<br />
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DR, Rands E, Seolniek EM (1977) Helper independent<br />
transformation by unintegrated Harvey sareoma<br />
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WL, Blair DG, Oskarsson M, Vande Woude GF<br />
(1980) Two regions of the Moloney leukemia virus<br />
genome are required for effieient transformation by<br />
sre/sare. In: Fields B, Jaeniseh R, Fox C (eds)<br />
Animal virus geneties ICN-UCLA symposia on<br />
moleeular and eellular biology. Aeademic Press,<br />
New York - MeClements WL, Dhar R, Blair DG,<br />
Enquist LW, Oskarsson M, Vande Woude GF (to be<br />
published a) The terminal repeats of integrated<br />
Moloney sareoma provirus are like baeterial insertion<br />
sequenee (IS) elements. Cold Spring Harbor<br />
Symp Quant Biol 45 - MeClements WL, Enquist<br />
LW, Oskarsson M, Sullivan M, Vande Woude GF (to<br />
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eoliphage ?.murine sareoma virus recombinants and<br />
its use in the identifieation of a retrovirus integration<br />
site. J Virol 35 - Oskarsson M, MeClements WL,<br />
Blair DG, Maizel JV, Vande Woude GF (1980)<br />
Properties of a normal mouse eell DNA sequenee<br />
(sare) homologous to the sre sequenee of Moloney<br />
sareoma virus. Scienee 207: 1222-1224 - Sherr CJ,<br />
Fedele LA, Oskarsson M, Maizel J, Vande Woude<br />
GF (1980) Moleeular cloning of Snyder-Theilen<br />
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studies of feline sarcoma virus with its natural helper<br />
and Moloney sareoma virus. J Virol 24:200-212<br />
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