A Drosophila teissieri I-element retrotransposon's ORF1p shows RNA binding cis-preference in the D. melanogaster female germline.

The transposable I-element from Drosophila melanogaster encodes an RNA-binding protein ORF1p required for its retroansposition. ORF1p binds single-stranded DNA and RNA in vitro nonspecifically. If this nonspecific RNA binding occurs in the germline, then we hypothesize that it plays a role in the production of heritable retrocopies of genes other than the I-element. The goal of this study was to test this hypothesis by investigating the specificity of ORF1p RNA binding in the female germline. To this end, we cloned a D. teissieri I-element. We first tested D. melanogaster strains transgenic for this element for its RNA and protein expression, and its transposition, and demonstrated that it has similar properties to those reported for previously isolated D. teissieri and D. melanogaster I-elements. Then, using RNA immunoprecipitation of epitope-tagged HAORF1p from ovary extracts, followed by high-throughput sequencing (RIP-seq), we found that HAORF1p binds RNA in cis with high specificity. Therefore, the I-element ORF1p does not appear to play a role in generating retrocopies by binding host cellular RNAs in trans in the female germline, unless it binds these RNAs rarely or with low affinity.