Terminal retrotransposons activate a subtelomeric white transgene at the 2L telomere in Drosophila

Genetically marked P elements inserted into the subtelomeric satellites of Drosophila show repression and variegation of the reporter gene. One such w hite(+) reporter, inserted between the subtelomeric satellite and the termi nal HeT-A array in the left arm of chromosome 2 (2L), is sensitive to its c ontext; changes in the structure of the telomere region can be identified b y changes in eye color. Addition of HeT-A or TART elements to the 2L termin us increases w(+) expression, and loss of sequence from the end decreases e xpression. This indicates that the telomeric retrotransposons in Drosophila have an activating influence on the repressed subterminal reporter gene. C hanges in eye color due to altered expression of the transgene also allow t he detection of interactions between homologous telomeres. The 2L arms that terminate in long HeT-A/TART arrays showed increased expression of the sub terminal w(+) transgene when the terminal repeats on the homologue are abse nt or markedly shorter. We propose that the chromatin structure of the term inal HeT-A/TART array and the activity of a putative promoter/enhancer elem ent on HeT-A are affected by telomeric interactions. Such trans-activation may reflect control over HeT-A transcription and, thus, transposition activ ity.