P-element homologous sequences are tandemly repeated in the genome of Drosophila guanche

Abstract

In Drosophila guanche, P-homologous sequences were found to be located in a tandem repetitive array (copy number: 20-50) at a single genomic site. The cytological position on the polytene chromosomes was determined by in situ hybridization (chromosome O: 85C). Sequencing of one complete repeat unit (3.25 kilobases) revealed high sequence similarity between the central coding region comprising exons 0 to 2 and the corresponding section of the Drosophila melanogaster P element. The rest of the sequence has diverged considerably. Exon 3 has no coding function and the inverted repeats have disappeared. The P homologues of D. guanche apparently have lost their mobility but have retained the coding capacity for a protein similar to the 66-kDa P-element repressor of D. melanogaster. Divergence between different repeat units indicates early amplification of the sequence at this particular genomic site. The presence of a common P-element site at 85C in Drosophila subobscura, Drosophila madeirensis, and D. guanche suggests that clustering of the sequence at this location took place before the phylogenetic radiation of the three species.