Competition between R1 and R2 transposable elements in the 28S rRNA genes of insectsYe J. · Pérez-González C.E. · Eickbush D.G. · Eickbush T.H.
Department of Biology, University of Rochester, Rochester, NY (USA)
R1 and R2 are non-LTR retrotransposons that insert in the 28S rRNA genes of arthropods. R1 elements insert into a site that is 74 bp downstream of the R2 insertion site, thus the presence of an R2 in the same 28S gene may inhibit the expression of R1. Consistent with such a suggestion, the R1 elements of Drosophila melanogaster have a strong bias against inserting into 28S genes already containing an R2 element. R2 elements, on the other hand, are only 2–3 fold inhibited from inserting into a 28S gene already containing an R1. D. melanogaster R1 elements are unusual in that they generate a 23-bp deletion of the target site upstream of the insertion. Using in vitro assays developed to study R2 integration, we show that the presence of R1 sequences 51 bp downstream of the R2 insertion site changes the nucleosomal structure that can be formed by the R2 target site. The R2 endonuclease is inhibited from cleaving these altered nucleosomes. We suggest that R1 elements have been selected to make this large deletion of the 28S gene to block the insertion of an upstream R2 element. These findings are consistent with the model that R1 and R2 are in competition for the limited number of insertion sites available within their host’s genome.
Current address of C.E.P.-G.: National Institutes of Health, Bethesda, MD (USA)
Request reprints from: Dr. Thomas H. Eickbush, Department of Biology
University of Rochester, Rochester, NY 14627 (USA)
telephone: +1-585-275-7247; fax: +1-585-275-2070
This research was supported by National Science Foundation grant MCB-9974606 and National Institutes of Health grant GM42790.
Manuscript received 16 September 2003;
accepted in revised form for publication by J.-N. Volff 13 January 2004.
Number of Print Pages : 8
Number of Figures : 5, Number of Tables : 0, Number of References : 38
Cytogenetic and Genome Research
Vol. 110, No. 1-4, Year 2005 (Cover Date: 2005)
Journal Editor: H.P. Klinger, Bronx, N.Y.; M. Schmid, Würzburg
ISSN: 1424–8581 (print), 1424–859X (Online)
For additional information: http://www.karger.com/cgr