A. Kalmykova et al., Retrotransposon 1731 in Drosophila melanogaster changes retrovirus-like expression strategy in host genome, GENETICA, 107(1-3), 1999, pp. 73-77
Earlier related to parasitic elements, retrotransposons of eukaryotes have
been demonstrated to participate in general cell processes such as chromoso
me repair and evolution of gene expression (Teng et al., 1996; McDonald, 19
93). Here, we report the existence of two class of genomic copies of retrot
ransposon 1731 with different expression strategies, one of which might be
driven by natural selection. The first class uses conventional translation
frameshifting known to ensure expression of revere transcriptase (RT) open
reading frame (ORF), depending on the efficiency of frameshifting. The bulk
of genomic copies are related to the second class where the frameshift is
prevented as a result of the substitution of a rare codon recoginsing rare
tRNA by a codon preferred by host genome, whereas the RT ORF is restored by
downstream single nuclotide deletion. We suggest that natural selection ha
s driven the switching of 1731 expression strategy from retrovirus-like to
the fussion-ORF expression. This observation is in accordance with the dete
ction in testes of fused Gag-RT polypetide encoded by 1731. The abundance o
f RT in testes may serve for normal development of host tissue.