# Institute of Molecular Biology and Biotechnology, FORTH, 71110 Heraklion, Crete, % Biology Dept., Brandeis University, Waltham MA 02254, USA,
Octopamine is one of the major neuroactive molecules in Drosophila and it is likely to be involved in important behaviors of the fly. We have been interested in studying its function using as a tool the molecular genetics of the enzymes involved in its biosynthetic pathway. For this purpose, we have cloned the gene coding for Tyramine B-hydroxylase (TBH) enzyme which catalyses the final step in the biosynthesis of octopamine. We recently reported (Monastirioti et al. 1996, J. Neuroscience 16, 3900-3911) on the cloning and the initial molecular and expression analysis of this gene. In addition we created null mutations at the Tbh locus which resulted in complete absence of the protein and blockage of the octopamine biosynthesis. Mutant females are sterile because even though they mate, they retain fully developed eggs, a defect which can be rescued if these females are fed on a octopamine-supplemented food. In order to create mutations at the Tbh locus different P-M mutagenesis screenings were performed. Several null as well as hypomorphic mutations were created and currently, studies on the molecular, immunocytochemical and behavioral characterization of the mutant lines are in progress.