We isolated forms of enveloped vaccinia virus from infected HeLa cells to obtain membranes for the analysis of
lipids of the cis-Golgi network and trans-Golgi network. The intracellular mature virus obtains its envelope by wrapping itself in the membranes of the cis-Golgi network. A fraction of these virions then acquires a second envelope by enwrapping trans-Golgi network membranes to form the intracellular enveloped virus.
Lipids were analyzed by high performance thin layer chromatography and digital densitometry to establish a steady-state
lipid profile of viral membranes, which should reflect the compositions of the 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,
semilysobisphosphatidic acid, was present in significant amounts in
vaccinia envelopes.
Semilysobisphosphatidic acid was present in similar levels in infected and uninfected cells, and was therefore not induced by
vaccinia infection. Subcellular fractionation of HeLa cells indicated that the recovery of
semilysobisphosphatidic acid paralleled the recovery of a Golgi marker. Furthermore, a
lipid species that comigrated with
semilysobisphosphatidic acid was also present in
lipids extracted from highly purified, intact Golgi complexes from rat liver. Together, these results suggest that
semilysobisphosphatidic acid is a normal component of Golgi membranes.