TheChironomus(Camptochironomus)tentansgenome contains two non-LTR retrotransposons

Abstract

A cDNA library from salivary gland cells of Chironomus tentans was screened with a probe containing the NLRCth1 non-LTR (long terminal repeat) retrotransposon from Chironomus thummi. Several positive clones were obtained and one of them, p62, was characterized by in situ hybridization and sequencing. The sequencing analysis showed that this clone contained a 4607 bp nucleotide sequence of a new transposable element that hybridized in situ to more than 100 sites over all four C. tentans chromosomes. The detailed analysis of this sequence revealed the presence of the 3′-end of open reading frame 1 (ORF1), a complete ORF2, and a 1.3-kb 3′-end untranslated region (UTR). The new element has been designated NLRCt2 (non-LTR retrotransposon 2 from C. tentans). A comparison of the nucleotide sequences of NLRCth1 and NLRCt2 showed 30% similarity in the region of ORF1 and 70% similarity in the region of ORF2. Based on the results of Southern blot analysis, two transposable elements have been found in the C. tentans genome, one of which is identical to NLRCth1 from C. thummi. This may be explained by horizontal transmission. The second element, NLRCt2, has been found in two different forms in the C. tentans genome. These can be distinguished by the presence of the 1.3-kb 3′-end UTR in one of the forms. Since the cDNA clone investigated was isolated from a tissue-specific cDNA library, the data showed that NRLCt2 is expressed in somatic cells.Key words: Chironomus, non-LTR retrotransposon, in situ hybridization, reverse transcriptase, horizontal transmission.