Extrachromosomal supercoiled circular copies of mobile dispersed genetic elements mdg1, mdg3 and copia have been isolated from 67J25D and Kc lines of cultured Drosophila melanogaster cells. With the exception of the copia element in the line Kc, all circular molecules contain only one long terminal repeat. Both whole-length circular copies and molecules with deletion from the internal segment of the copia element have been detected in the line 67J25D. Mdg3-specific circular molecules in the line Kc are represented by the deleted molecules only. Similar copies of mdg3 are also present in chromosomal DNA of flies and cultured cells. The analysis of the mdg3 transcription in both cell lines suggests that extrachromosomal molecules of mdg may be created by reverse transcription.
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