TRANSCRIPTION OF GYPSY ELEMENTS IN A Y-CHROMOSOME MALE-FERTILITY GENEOF DROSOPHILA-HYDEI

We have found that defective gypsy retrotransposons are a major consti tuent of the lampbrush loop pair Nooses in the short arm of the Y chro mosome of Drosophila hydei. The loop pair is formed by male fertility gene Q during the primary spermatocyte stage of spermatogenesis, each loop being a single transcription unit with an estimated length of 260 kb. Using fluorescent in situ hybridization, we show that throughout the loop transcripts gypsy elements are interspersed with blocks of a tandemly repetitive Y-specific DNA sequence, ayl. Nooses transcripts c ontaining both sequence types show a wide size range on Northern blots , do not migrate to the cytoplasm, and are degraded just before the fi rst meiotic division. Only one strand of ayl and only the coding stran d of gypsy can be detected in the loop transcripts. However, as cloned genomic DNA fragments also display opposite orientations of ayl and g ypsy, such DNA sections cannot be part of the Nooses. Hence, they are most likely derived hom the flanking heterochromatin. The direction of transcription of ayl and gypsy thus appears to be of a functional sig nificance.