TEMPERATURE-SENSITIVE EXPRESSION OF DROSOPHILA NEURONAL NICOTINIC ACETYLCHOLINE-RECEPTORS

Heterologous expression of cloned Drosophila nicotinic acetylcholine r eceptor (nAChR) subunits indicates that these proteins misfold when ex pressed in mammalian cell lines at 37 degrees C. This misfolding can, however, be overcome either by growing transfected mammalian cells at lower temperatures or by the expression of Drosophila nAChR subunits i n a Drosophila cell line. Whereas the Drosophila nAChR beta subunit (S BD) cDNA, reported previously, lacked part of the SBD coding sequence, here we report the construction and expression of a full-length SBD c DNA. We have examined whether problems in expressing functional Drosop hila nAChRs in either Xenopus oocytes or mammalian cell lines can be a ttributed to an inability of these expression systems to assemble corr ectly Drosophila nAChRs, Despite expression in what might be considere d a more native cellular environment, we have been unable to detect fu nctional nAChRs in a Drosophila cell line unless Drosophila nAChR subu nit cDNAs are coexpressed with vertebrate nAChR subunits. Our results indicate that the folding of Drosophila nAChR subunits is temperature- sensitive and strongly suggest that the inability of these Drosophila nAChR subunits to generate functional channels in the absence of verte brate subunits is due to a requirement for coassembly with as yet unid entified Drosophila nAChR subunits.