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In the article, "Mutations in Drosophila Enabled and Rescue by Human Vasodilator-stimulated Phosphoprotein (VASP) Indicate Important Functional Roles for Ena/VASP Homology Domain 1 (EVH1) and EVH2 Domains" (Mol. Biol. Cell [1998]. 9, 2157-2171), Ping Hua was listed in the acknowledgments but should have been included as an author. The author line should read Shawn M. Ahern-Djamali, Allen R. Comer, Christiane Bachmann, Andrew S. Kastenmeier, Srinevas K. Reddy, Ping Hua, Mary C. Beckerle, Ulrich Walter, and F. Michael Hoffmann.

Cover  Virus-like particles in a yeast cell. They were created experimentally by Gerry Fink and coworkers (Garfinkel, D.J., Boeke, J.D., and Fink, G.R. [1985]. Cell 42, 507-517) by attaching an activated promoter to the coding sequence of a yeast Ty transposable element, thus demonstrating directly the relationship between retrotransposons and retroviruses.

In 1970 Howard Temin proposed the protovirus hypothesis that RNA tumor viruses evolved from movable genetic elements in cells (see Temin, H. [1980]. Cell 21, 599-600). By the mid-1980s enough structural and sequence information had been collected to demonstrate remarkable similarity between retroviruses and one class of transposable elements, now called the retrotransposons. The similarities include long terminal repeats, sequences that can serve as tRNA primer binding sites, and transposon genes that show similarity to the retroviral gag and pol genes. Although these similarities could be used equally well to support the hypothesis that retroviruses originated from cellular elements, or the hypothesis that elements originated from viruses, they did show that one class of frequently encountered DNA repeat element had a close evolutionary relationship with an important class of virus.

Just how close was demonstrated by Fink and his colleagues in 1985. Earlier work with Drosophila copia elements, which like yeast Ty1 elements are members of the retrotransposon family, showed that copia-homologous RNA could be found in retrovirus-like particles (Shiba, T., and Saigo, K. [1983]. Nature 302, 119-124.) To turn this correlation into a causal analysis, Fink and his collaborators attached a GAL1 promoter, inducible by galactose, to a Ty element coding sequence and introduced this to yeast on a plasmid. This allowed, by change from a glucose- to a galactose-containing medium, experimental activation of Ty transcription. They showed that this activation resulted in increased frequency of transposition, that transposition involved an RNA intermediate, that the Ty element encoded a reverse transcriptase, and that activation of a Ty element leads to formation of virus-like particles.

This work not only demonstrated unequivocally the functional relationship of retrotransposons to retroviruses, but also showed that the yeast Ty1 elements were capable of transposition in other than evolutionary timescalesa point not accepted at the time of the experiments. This figure is reprinted with the permission of Cell Press (Garfinkel, D.J., Boeke, J.D., and Fink, G.R. [1985]. Ty element transposition: reverse transcriptase and virus-like particles. Cell 42, 507-517). Elliot Meyerowitz