The nanos promoter should induce maternal nurse cell expression, and also zygotic germ cell expression after the end of embryogenesis. The nanos 5' and 3' untranslated regions should cause the GAL4 mRNA to be localized to the posterior pole and to be translated only at the posterior pole. The observed pattern of expression is consistent with this in that GAL4 activity is found preferentially in the pole cells. There is also a transient activity found in the posterior endoderm primordium. Expression of lacZ and GFP has been observed in te primordial germ cells (pole cells) from stage 8 (germ band extending) throughout embryogenesis and into larval stages. GAL4 activity also appears to be present in the germ cells of the male testes, but does not appear present in the nurse cells. There appears to be consistent 'background' staining later in development beginning after stage 12, and this is most likely due to aberrant zygotic expression from the truncated nanos promoter as it is seen in several lines.