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Chapter 11 : Reprint of Shimotohno, Mizutani, and Temin's 1980 Paper on the Similarity of the Structures of Retroviral Proviruses to That of Transposable Elements
Reprint of Shimotohno, Mizutani, and Temin's 1980 Paper on the Similarity of the Structures of Retroviral Proviruses to That of Transposable Elements, Page 1 of 2< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555818302/9781555810986_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555818302/9781555810986_Chap11-2.gif
In the paper by Shimotohno, Mizutani, and Temin, the authors describe the identification, cloning, and sequencing of the long terminal repeats (LTRs) and the abutting cellular DNA of infectious proviruses of spleen necrosis virus. The LTRs of retroviruses are direct repeats of sequences of DNA at the ends of the provirus. The 3' terminus of the 5' LTR should therefore be identical to the 3' terminus of the intact provirus; similarly, the 5' terminus of the 3' LTR should be identical to the 5' terminus of the intact provirus. A knowledge of this structure along with the determined DNA sequences allowed Howard and his colleagues to identify the junctions of proviral DNA and the cellular DNA into which the proviral DNA had integrated. They made two striking observations: the proviral DNA lost two nucleotides from each end prior to its integration, and five nucleotides of the cellular DNA were duplicated at the site of integration. These two observations contributed substantively to the basis for their hypothesis that retroviruses have evolved from cellular movable genetic elements that often share the features. Howard Temin continued to study and elucidate the mechanism of retroviral replication through genetic and biochemical dissections of the products of replication during a single cycle of infection. These studies allowed him to validate his provirus hypothesis and to reconstruct pathways by which retroviruses assimilate proto-oncogenes. The resemblance of the provirus to transposable elements indicates that retroviruses may have evolved from such elements.