Dosage compensation of the copia retrotransposon in Drosophila melanogaster.

Dosage compensation in Drosophila has been studied at the steady state RNA level for several single-copy genes; however, an important point is addressed by analyzing a repetitive, transposable element for dosage compensation. The two issues of gene-specific cis control and genomic position can be studied by determining the extent of dosage compensation of a transposable element at different chromosomal locations. To determine whether the multicopy copia transposable element can dosage compensate, we used the X-linked white-apricot (wa) mutation in which a copia element is present. The extent of dosage compensation was determined for the white and copia promoters in larvae and adults in two different genomic locations of the wa allele. We conclude that copia is able to dosage compensate, and that the white promoter and the copia promoter are not coordinate in their dosage compensation abilities when assayed under these various conditions. Thus, two transcriptional units, one within the other, both of which are able to dosage compensate, do so differently in response to developmental stage and genomic position.