ABSTRACT
Retrotransposons constitute an extensively distributed family of eukaryotic transposable elements. The retrotransposons share a number of structural features which reflect the mechanism by which new copies of the transposon are generated; this process is similar to that of retroviral reverse transcription and integration. The marked progeny transposons occasionally showed evidence of heterogeneity with respect to the parental plasmid-borne element. A highly speculative but stimulating model for the retrotransposition of the DIRS1 element of Dictyostelium discoideum has been proposed by Cappello et al. The transcription of IAP elements is very much elevated in most tumor cell lines. This corresponds with original observations on the presence of Intracistemal A-particle particles in various cell lines. All elements of a family are probably affected transcriptionally by the sequences adjacent to them. Retrotransposons often are associated with the ability to activate the transcription of adjacent genes. Moreover, this activation is often under the same type of regulation as is the retrotransposon itself.
