MEMBRANE ASSOCIATION OF PHOSPHOLIPASE-C ENCODED BY THE NORPA GENE OF DROSOPHILA-MELANOGASTER

Severe mutations within the norpA gene of Drosophila abolish the photo receptor potential and render the fly blind by deleting phospholipase C, an essential component of the phototransduction pathway. To study t he membrane association of phospholipase C, we have utilized biochemic al assays of phospholipase C activity, which predominant measurable ph ospholipase C activity in head homogenates has been shown to be encode d by norpA, as well as antisera generated against the major gene produ ct of norpA to examine its subcellular distribution before and during phototransduction. We find that both phospholipase C activity and the norpA protein are predominantly associated with membrane fractions in heads of both light- and dark-adapted flies. Moreover, phospholipase C activity as well as norpA protein can be easily extracted from membra ne preparations of light- or dark-adapted flies using high salt, indic ating that the norpA protein is peripherally localized on the membrane . These data suggest that the norpA encoded phospholipase C of Drosoph ila is a permanent peripheral membrane protein. If this is indeed the case, then it would mean that the reversible redistribution of phospho lipase C from the cytosol to the membrane, as observed in epidermal gr owth factor receptor stimulation of mammalian phospholipase C gamma, i s not a universal mechanism utilized by all types of phosphatidylinosi tol-specific phospholipase C.