CLONING AND FUNCTIONAL EXPRESSION OF A NEURONAL CALCIUM-CHANNEL BETA-SUBUNIT FROM HOUSE-FLY (MUSCA-DOMESTICA)

The primary structure of a calcium channel beta subunit (beta(M)) from housefly (Musca domestica) has been deduced by cDNA cloning and seque nce analysis. The open reading frame encodes a 441-amino acid polypept ide with a calculated molecular mass of 48,755 Da. Whole-mount in situ hybridization indicates that beta(M) mRNA is predominantly expressed in neuronal tissues. Transcription of beta(M) mRNA is evident from sta ge 13/14 of embryogenesis up to adulthood. Different expression patter ns of splice variants were found in larvae and in adult fly heads. Ami no acid identity between beta(M) and mammalian beta subunits is lower (66-68%) than within mammalian beta subunits (74-80%). Calculation of a phylogenetic tree indicates that beta(M) is an ancestral form of the four distinct beta subunit gene products identified in mammalian tiss ues so far. Despite these sequence differences, beta(M) is able to enh ance endogenous calcium channel activity in Xenopus laevis oocytes as well as dihydropyridine binding to membranes from COS 7 cells transfec ted with rabbit heart alpha(1) cDNA in the same manner as was previous ly shown for mammalian beta subunits.