Secondary piRNAs also differs strongly in the strains studied and the low level of Ulysses secondary piRNAs in strain 9 may reflect the absence of ping-pong amplification loop necessary for Ulysses silencing. Interestingly, in testes a high level of Ulysses-derived antisense piRNAs was found, and, surprisingly, this fraction is predominantly homologous to LTRs of this TE. This phenomenon might resemble the different functional activities of GW786034 Argonaute group proteins in the testes and ovaries. Alternatively, LTRhomologous antisense piRNAs may be coming from a solo Ulysses LTRs located in a piRNA-producing cluster functioning only in testes. Despite the fact, that Penelope is one of the most abundant transposon in the genome of D. virilis with more than 50 copies in strain 160, we did not detect transpositions of the element to chromosome 6. This may result from either Penelope transposition preferences or from the recently described peculiar chromatin structure of chromosome 6 in D.virilis. It is also tempting to speculate that such transposition preferences in avoiding of heterochromatic regions and perhaps piRNA loci might be a reason for a continuing transposition activity of this element in strain 160 of D. virilis as well as in transgenic D. melanogaster strains transformed with full-size Penelope. Comparing the general localization of hybridization sites specific for the studied TEs in the D. virilis genome enables us to conclude that the observed distribution is not random, and there are sites where two or three TEs are found. Probably these sites represent “hot spots�?or “nests�?of transposons previously described both in the D. virilis and D. melanogaster genomes. In particular, we do not rule out that at least one of such hot spots, i.e. 49F that coincides with the coordinates of cluster #3, might serve as a putative flamenco piRNA locus in D. virilis genome that produces the most abundant fraction of sense oriented transposon-homologous piRNAs in D. virilis genome. In the present investigation we did not monitor intrastrain transposition of other TEs mobilized by dysgenic crosses which may represent another interesting avenue of future research, because there are at least two other elements, Paris and Helena, which are abundant in strain 160, but absent or found in small numbers in strain 9. Recently, based upon the analysis of maternal inheritance of small RNAs in various systems of D. melanogaster HD, it was suggested that piRNAs have an important role in the regulation of the syndrome by homology-dependent TE silencing. In D. virilis Penelope-derived small RNAs were also implicated in HD syndrome regulation. Moreover, we speculate that Penelope is transpositionally active in strain 160, because, for some reason in this particular quite exceptional strain, small RNAs are represented predominantly by siRNAs.