The palindromic LTR-LTR junction is not an efficient substrate for proviral integration, suggesting a linear or more exotic DNA intermediate is the true precursor.
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Questions LTR-LTR junction efficiency for integration; leaves open linear DNA as the authentic retroviral precursor in animal models.
We generated viral constructs to test the hypothesis that the major substrate on retroviral DNA that is utilized for proviral DNA integration is the palindromic sequence, termed the LTR-LTR junction, normally present in circular molecules formed by joining the two termini of linear proviral DNA. Recombinant viral genomes were built which carried a selectable marker and an extra copy of the LTR-LTR junction from a cloned circular provirus. The junction sequence in each case was positioned such that its use during integration would lead to an easily detected, aberrantly integrated proviral DNA. Analysis of DNA from cells infected with the virus constructs showed that the introduced junction sequence is used at least 1,000-fold less efficiently than the natural sequences at the ends of the genome. This suggests that a linear or more exotic DNA intermediate is most likely the true precursor for the integration reaction.
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Lobel et al. (1989) studied this question.
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