THE ENVELOPE OF VACCINIA VIRUS REVEALS AN UNUSUAL PHOSPHOLIPID IN GOLGI-COMPLEX MEMBRANES

We isolated two forms of enveloped vaccinia virus from infected HeLa c ells to obtain membranes for the analysis of lipids of the cis-Golgi n etwork and trans-Golgi network, The intracellular mature virus obtains its envelope by wrapping itself in the membranes of the cis-Golgi net work, A fraction of these virions then acquires a second envelope by e nwrapping trans-Golgi network membranes to form the intracellular enve loped virus, Lipids were analyzed by high performance thin layer chrom atography and digital densitometry to establish a steady-state lipid p rofile of viral membranes, which should reflect the compositions of th e cis-Golgi network and trans-Golgi network, Phosphatidyl-inositol was slightly enriched in the cis-Golgi network of HeLa cells, whereas the trans-Golgi network showed a minor increase in phosphatidylserine and sphingomyelin. Similarly, cholesterol was only slightly more abundant in the trans-Golgi compared to the cis-Golgi, An unusual lipid, semil ysobisphosphatidic acid, was present in significant amounts in vaccini a envelopes, Semilysobisphosphatidic acid was present in similar level s in infected and uninfected cells, and was therefore not induced by v accinia infection. Subcellular fractionation of HeLa cells indicated t hat the recovery of semilysobisphosphatidic acid paralleled the recove ry of a Golgi marker, Furthermore, a lipid species that comigrated wit h semilysobisphosphatidic acid was also present in lipids extracted fr om highly purified, intact Golgi complexes from rat liver. Together, t hese results suggest that semilysobisphosphatidic acid is a normal com ponent of Golgi membranes.