CHARACTERIZATION AND GENETIC ORGANIZATION OF FULL-LENGTH COPIES OF A LINE RETROPOSON FAMILY DISPERSED IN THE GENOME OF CULEX-PIPIENS MOSQUITOS

Many full-length copies of a long interspersed repetitive element fami ly, designated Juan-C, are reiterated in the genome of Culex pipiens m osquitoes. The complete Juan-C elements have a length of 4.48 kb. They are terminated at one end with an adenosine-rich sequence preceded wi th an AATAAA polyadenylation signal, lack terminal repeats and cause d uplication of the host DNA at the site of their integration. Full-leng th Juan-C copies display two long open reading frames potentially enco ding two proteins. The first one includes a domain typical of nucleic- acid-binding proteins, while the second resembles reverse transcriptas es. Therefore, Juan-C elements are similar to LINE retroposons in thei r overall genetic organization and can probably be transposed by rever se transcription of an RNA intermediate. Juan-C elements are most simi lar in their sequence and coding potential to the Juan-A elements whic h are reiterated in mosquito species belonging to the genus Aedes. The y also display homologies with some Drosophila LINEs such as Jockey, s uggesting that all these elements have arisen from a common precursor. Nearly identical full-length Juan-C copies are amplified in C. pipien s strains from different continents. This finding that Juan-C retropos ons reiterated in different strains form an homogeneous family is inte rpreted to indicate that these elements have spread recently in the C. pipiens species.