Authentic reverse transcriptase is coded by jockey, a mobile Drosophila element related to mammalian LINEs.

Abstract

The mobile element jockey is similar in structural organization and coding potential to the LINEs of various organisms. It is transcribed at different stages of Drosophila ontogenesis. The Drosophila LINE family includes active transposable elements. Current models for the mechanism of transposition involve reverse transcription of an RNA intermediate and utilization of element‐encoded proteins. As demonstrated here, a 2.23 kb DNA fragment from the region of jockey encoding the putative reverse transcriptase was stably introduced into an expression system under inducible control of the Escherichia coli lac regulatory elements. We describe the expression of the 92 kDa protein and identify this polypeptide alone as the authentic jockey reverse transcriptase based on some of its physical and enzymic properties. The jockey polymerase demonstrates RNA and DNA‐directed DNA polymerase activities but lacks detectable RNase H, has a temperature optimum at 26 degrees C, requires Mg2+ or Mn2+ as a cofactor and is inactivated by sulphydryl reagent. The enzyme prefers poly(rC) and poly(rA) as template and ‘activated’ DNA is not effective.

Transcriptomic responses of the endangered freshwater mussel Margaritifera margaritifera to trace metal contamination in the Dronne River, France

“…Fifty-four transcripts are found in these GO categories (Online Resource 7) out of which 11 are homologous of reverse transcriptases encoded by retrotransposons related to the LINE-1 family (Ivanov et al 1991). As dynamic components of genomes, retrotransposons are a source of genetic/epigenetic variation and novelty and are increasingly seen as implicated in fundamental genomic functions, in both normal and pathological contexts (Sciamanna et al 2016).…”

A complete full-length non-LTR retrotransposon, BMC1, on the W chromosome of the silkworm, Bombyx mori.

“…LINEs are generally 5 -8 kb long, but most are functionally inactive due to truncations at the 5' end, rearrangements, and nonsense mutations (Capy et al, 1998). The mammalian L1 elements and the Drosophila elements I, F, and Jockey are good examples of non-LTR retrotransposons (Pelisson et al, 1991;Ivanov et al, 1991). Approximately 100,000 L1 elements exist in the human genome (Fanning and Singer, 1987) and these elements make up at least 15% of it (Smit and Riggs, 1996).…”

Downstream 28S Gene Sequences on the RNA Template Affect the Choice of Primer and the Accuracy of Initiation by the R2 Reverse Transcriptase

“…The distinguishing features of these elements are that they encode an open reading frame with homology to reverse transcriptases but are not flanked by the terminal repeats associated with all retroviruses and all retrotransposable elements of the copia/Ty1 and gypsy/Ty3 groups (2,11,34). Evidence that the non-LTR retrotransposons encode a functional reverse transcriptase has been obtained for the jockey element of Drosophila melanogaster (18), CRE1 of Crithidia fasciculata (13), L1 of humans (26), and R2 of Bombyx mori (25). Direct evidence that these elements utilize an RNA intermediate in their mobility has been obtained from experiments in which inserted intron sequences were found to be accurately removed during the formation of new copies of the I element of D. melanogaster (28) and the L1 element of mice (12,20).…”