Using each one of the four open reading frames in the P transposable element of Drosophila melanogaster, computer search of homology was carried out against the protein sequence data base of NBRF version 4. A deduced polypeptide of about 210 residues in ORF1 of the P element appears to have a significant homology with the resolvases of bacterial transposable elements Tn3 and γδ. The polypeptide seems to possess a region consisting of 22 amino acid residues having homology with DNA-binding fold of the resolvases of the bacterial transposons Tn3 and γδ, which are known to have a repressor function of the transposable elements. There are a nine base pair region in ORF3 and also in the 31 base pair inverted terminal repeat of the P element having homology with a site in the promoter region of the Tn3 and also of γδ at which the resolvases bind and suppress transcription of transposases. Based on these findings, it was suggested that the ORF1 might code a resolvase protein which mediates site-specific recombination and also suppresses the transposition of the P by binding at a specific site in the ORF3 or in the terminal repeat. It was also suggested that the whole P might code a transposase.
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