3/17/2023 0 Comments Ifactor 2 insideRetrotransposons of the second type have an adenine-rich sequence at the 3′ end of the coding strand but no terminal repeats. The first, the retroviral-like or LTR elements, have long direct repeats at their termini and contain open reading frames homologous to the gag and pol genes of retroviruses with some having a third open reading frame equivalent to an env gene ( Pelisson et al., 1994 Song et al., 1994). Retrotransposons are eukaryotic transposable elements that transpose by reverse transcription of an RNA intermediate ( Boeke and Corces, 1989) and are of two types. This may be generally true for the product of the first open reading frame of LINE-like elements. These results suggest that this protein may associate with the RNA transposition intermediates of the I factor to form particles that enter the nucleus during transposition and that it may stimulate both the priming of reverse transcription and integration. This protein can also accelerate the annealing of complementary single-stranded oligonucleotides. The ORF1 protein expressed in either E.coli or Spodoptera cells forms high molecular weight structures that require the region of the protein including the CCHC motif for their formation. The properties of deletion derivatives of the protein indicate that more than one region is responsible for DNA binding and that the CCHC motif is not essential for this. We have expressed this protein in Escherichia coli and Spodoptera frugiperda cells and have shown that it binds both DNA and RNA but without any evidence for sequence specificity. The amino acid sequence encoded by the first of these, ORF1, includes the motif CX 2CX 4HX 4C that is characteristic of the nucleocapsid domain of retroviral gag polypeptides followed by a copy of the slightly different sequences CX 2CX 4HX 6C and CX 2CX 9HX 6C. Complete I factors contain two open reading frames. I factors are members of the LINE-like family of transposable elements and move by reverse transcription of an RNA intermediate.
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