Here we investigated dynamic properties of the piNG-body, large perinuclear 
granule that was discovered previously in spermatocytes of Drosophila. The 
piNG-body contains ribonucleoprotein complexes involved in piRNA-silencing of 
genome repeats including transposons in premeiotic spermatocytes with aid of 
short piRNAs. Confocal microscopy of fixed and native preparations demonstrates 
that the piNG-body is mobile structure which does not occupy a stationary 
position near nuclear surface relative to chromosomal territories. FRAP-analysis 
reveals a high exchange rate of RNA helicase Vasa in the piNG-body and small 
perinuclear granules with the cytozol Vasa pool. Disruption of microtubule 
assembly of cytoskeleton does not affect to stability of the piNG-body and small 
granules. We suppose that the combination of piNG-body mobility and permanent 
molecular exchange of Vasa protein provides an efficient "scanning" of total 
volume of the cytoplasm of primary spermatocytes and timely recognition and 
destruction of unwanted transcripts of the repetitive elements of genome.