COEXPRESSION OF 2 ODORANT-BINDING PROTEIN HOMOLOGS IN DROSOPHILA - IMPLICATIONS FOR OLFACTORY CODING

Odorant-binding proteins (OBPs) are small soluble proteins present in the aqueous medium surrounding olfactory receptor neurons. Their funct ion in olfaction is still unknown: they have been proposed to facilita te the transit of hydrophobic molecules to olfactory receptors, to dea ctivate the odorant stimulus, and/or to play a role in chemosensory co ding. In this study we examine the genomic organization and expression patterns of two olfactory-specific genes (OS-E and OS-Fl of Drosophil a melanogaster, the products of which are members of a protein family in Drosophila sharing sequence similarity with moth OBPs. We show that the OS-E and OS-F transcription units are located <1 kb apart. They a re oriented in the same direction and display a similar intron-exon or ganization. Expression of both OS-E and OS-F proteins is restricted sp atially to the ventrolateral region of the Drosophila antenna. Within this region both OS-E and OS-F proteins are expressed within two diffe rent types of sensory hairs: in most, if not all, sensilla trichodea a nd in similar to 40% of the interspersed small sensilla basiconica. We consistently observe that OS-E and OS-F are coexpressed, indicating t hat an individual sensillum can contain more than one odorant-binding protein. The functional significance of the observed expression patter n and its implications for olfactory coding are discussed.