Temporal expression in heads of SG transgenic flies. Pairs of males carrying the same per allele were sectioned and stained with X-gal at opposite ZTs. In contrast to PER, which is highly abundant late at night (ZT24) and nearly undetectable by the end of the day (ZT12), the SG fusion protein shows no such fluctuations (compare ZT12 with ZT24). The reporter activity was at a constantly high level in PR cells, glia, and LNs inper⁺ andper⁰¹ genetic backgrounds, for both the SG3 and SG10 transgenic flies (data not shown forper⁰¹ SG10). The same results were obtained after staining SG transgenics with anti-β-GAL antibody (data not shown).