ADP-RIBOSYLATION FACTOR REGULATES SPECTRIN BINDING TO THE GOLGI-COMPLEX

Homologues of two major components of the well-characterized erythrocy te plasma-membrane-skeleton, spectrin (a not-yet-cloned isoform, beta I Sigma spectrin) and ankyrin (Ank(G119) and an approximate to 195-kD a ankyrin), associate with the Golgi complex, ADP ribosylation factor (ARF) is a small G protein that controls the architecture and dynamics of the Golgi by mechanisms that remain incompletely understood. We fi nd that activated ARF stimulates the in vitro association of beta I Si gma spectrin with a Golgi fraction, that the Golgi-associated beta I Sigma spectrin contains epitopes characteristic of the beta I Sigma 2 spectrin pleckstrin homology (PPI) domain known to bind phosphatidyli nositol 4,5-bisphosphate (PtdInsP(2)), and that ARF recruits beta I Si gma spectrin by inducing increased PtdInsP(2) levels in the Golgi, Th e stimulation of spectrin binding by ARF is independent of its ability to stimulate phospholipase D or to recruit coat proteins (COP)-I and can be blocked by agents that sequester PtdInsP(2), We postulate that a PH domain within beta I Sigma: Golgi spectrin binds PtdInsP(2) and acts as a regulated docking site for spectrin on the Golgi, Agents tha t block the binding of spectrin to the Golgi, either by blocking the P H domain interaction or a constitutive Golgi binding site within spect rin's membrane association domain I, inhibit the transport of vesicula r stomatitis virus G protein from endoplasmic reticulum to the medial compartment of the Golgi complex, Collectively, these results suggest that the Golgi-spectrin skeleton plays a central role in regulating th e structure and function of this organelle.