Fig. 6. Suppression of ectopic nos expression by GAL80. (A) GAL4^109-68 activates UAS-nos-tub3'UTR in a subset of cells in the CNS (dark shading). GAL4^109-68 may also activate UAS-nos-tub3'UTR at low levels or at unexamined times in EH cells (light shading with ‘?’). Ectopic synthesis of Nos in one or more cells of the GAL4^109-68 expression domain produces the adolescent phenotype. (B) Ubiquitous expression of GAL80 under control of the tubulin promoter (tubP-GAL80) blocks the ability of GAL4^109-68 to activate transcription of the UAS-nos-tub3'UTR transgene in all cells and suppresses the adolescent phenotype (Table 3). (C) The ability of GAL80 to block transcriptional activation by GAL4^109-68, as shown in B, was used to test whether GAL4^109-68 is indeed active in EH cells. Expression of GAL80 specifically in EH cells by EHups-GAL80 should block GAL4 activation of UAS-nos-tub3'UTR and suppress the adolescent phenotype only if GAL4^109-68 drives expression of UAS-nos-tub3'UTR in EH cells (Table 3).