A Golgi retention signal in a membrane-spanning domain of coronavirus E1 protein

Another, nonreceptor-mediated mechanism of retention is also conceivable . A structural change such as aggregation could occur when a protein arrives in a new compartment, preventing movement into transport vesicles. This type of retention has been demonstrated for many mutant proteins that fail to fold correctly after synthesis, resulting in retention in the ER (37) . The cis-Golgi is thought to differ from the ER in several ways, most notably in lipid composition The Journal of Cell Biology, Volume 115, 1991 and divalent cation concentration . The early Golgi is the first compartment where a newly synthesized protein comes into contact with glucosylceramide and sphingomyelin, which are synthesized there (12, 13) . In addition, the Cal+ concentration is presumed to be significantly lower than in the ER (3) . We are currently analyzing the oligomeric structure of the El protein and the mutant protein Om2,3 . Since Gml is found in an oligomer greater than 15S, the possibility exists that retention of these proteins occurs indirectly via aggregation. We are using both the El protein mutants and the Gml mutants to address the possible direct (receptor mediated) or indirect mechanisms of retention .