[Fine structure of long terminal repeats and stages of reverse transcription of mobile dispersed genes in Drosophila].

In Drosophila melanogaster cultured cells, RNA reverse transcription intermediate forms connected with initiation of minus and plus DNA strand synthesis (minus and plus strong-stop DNA) are detected for mobile dispersed genetic elements MDG1, MDG3 and MDG4 (gypsy). A comparative analysis of intermediate forms has proved that mdg elements pass the same stages of reverse transcription as retroviruses, revealing a complete similarity between intermediate products. It has also been established that these three mdg elements possess a common mechanism of reverse transcription, despite their structural differences. The length of the minus strong-stop DNA, that gives the position of the RNA start site, coincides with the data obtained from SI nuclease analysis of transcription initiation. SI mapping has also revealed that mdg RNA carries a repeated sequence R on its ends, similar to retroviral RNA molecules, and that mdg LTRs have a U3-R-U5 structure analogous to that of proretroviral LTRs. Transcription of mdg1, mdg3 and mdg4 is initiated within or immediately after the same sequence TCAGTPy. Neither TATA box nor CAAT box can be found in their characteristic positions upstream of the 5' ends of mRNA.