CM-GAG, A TRANSPOSABLE-LIKE ELEMENT REITERATED IN THE GENOME OF CULEX-PIPIENS MOSQUITOS, CONTAINS ONLY A GAG GENE

CM-gag elements constitute an homogeneous family of sequences that are reiterated in the genome of Culex pipiens strains from different cont inents. Apparently complete 1.75 kb CM-gag copies are flanked by targe t-site duplications and have a polyadenylation signal near their 3' en d. They potentially contain a unique gene encoding a putative protein that displays homologies with nucleic acid binding proteins and the ga g polypeptide of retroviruses and retrotransposons, but that does not encode a reverse transcriptase. CM-gag elements are similar in their g enetic organization to the telomeric transposable sequences Het-A from Drosophila melanogaster, but Southern-hybridization patterns indicate that the former are more probably dispersed in various areas of the m osquito genome. The homogeneity of CM-gag copies that are distributed worldwide suggests that they have most probably been amplified recentl y. Furthermore, selective constraints against amino acid changes have been acting on these sequences, suggesting that they need to encode th e gag-like protein to be incorporated into the chromosomes.