Regulated Gene Expression as a Tool for Analysis of Heterochromatin Position Effect in Drosophila.

Position effect variegation (PEV) is a perturbation of genes expression resulting from the changes in their chromatin organization due to the abnormal juxtaposition with heterochromatin. The exact molecular mechanisms of PEV remain enigmatic in spite of the long history of PEV studies. Here, we developed a genetic model consisting of PEV-inducing chromosome rearrangement and a reporter gene under control of the UAS regulatory element. Expression of the reporter gene could be regulated by adjustment of the GAL4 transactivator activity. Two UAS-based systems of expression control were tested - with thermosensitive GAL4 repressor GAL80ts and GAL4-based artificial transactivator GeneSwitch. Both systems were able to regulate the expression of the UAS-controlled reporter gene over a wide range, but GAL80ts repressed the reporter gene more efficiently. Measurements of the heterochromatin-mediated repression of the reporter gene in the GAL4+GAL80ts system point to the existence of a threshold level of expression, above which no PEV is observed.