Immunological and molecular characterization of G(oα)-like proteins in the Drosophila central nervous system

The α subunits of heterotrimeric G proteins are responsible for the coupling of receptors for a wide variety of stimuli to a number of intracellular effector systems. In the nervous system of vertebrates, high levels of a specific class of G protein (G(oα)) are expressed. The α subunit of G(o) serves as a substrate for modification by pertussis toxin (PTX). In this report, we demonstrate that the Drosophila heads contain high levels of a 40-kDa PTX substrate. Modification of this protein by PTX is modulated in a manner similar to that observed for vertebrate G proteins. The PTX substrate in Drosophila is also recognized specifically by antibodies raised against peptide sequences found specifically in vertebrate G(oα). Vertebrate G(oα) probes were used to identify a Drosophila cDNA coding for a potential PTX substrate with high sequence identity (82%) to vertebrate G(oα). An additional cDNA coding for a related G(oα) has also been isolated. The two cDNAs differ only in the 5'-untranslated and amino-terminal regions of the protein. This observation, in addition to Northern analysis, suggests that alternative splicing may generate a variety of G(oα)-like proteins in Drosophila. In situ hybridization of specific probes to tissue sections indicates that the mRNAs coding for G(oα)-like proteins in Drosophila are expressed primarily in neuronal cell bodies and, at lower levels, in the eyes.