Defining the Retention Signal in a Model Golgi Membrane Protein

Abstract

Specific sequences found in resident proteins of the endoplasmic reticulum (ER) and Golgi complex are believed to direct retention of these proteins in the appropriate compartment of the exocytotic pathway. Such “retention signals” have been identified at the carboxy-termini of both lumenal and membrane-bound ER resident proteins (reviewed by Pelham, 1991). We have been studying the targeting of Golgi membrane proteins using the E1 glycoprotein from the avian infectious bronchitis virus (IBV) as a model protein. This protein is targeted to cis Golgi membranes when expressed from cDNA in animal cells (Machamer et al, 1990). We previously determined that the first of the three membrane-spanning domains of the El protein contained Golgi targeting information (Machamer and Rose, 1987; Swift and Machamer, 1991). This first membrane-spanning domain (“m1”) can retain a plasma membrane protein (the vesicular stomatitis virus G protein) in the Golgi complex when inserted in place of the normal transmembrane domain. The chimeric protein (“Gm1”) is retained in the early Golgi complex suggesting that the ml domain is necessary and sufficient for the targeting of the IBV El protein to the cis Golgi complex (Swift and Machamer, 1991).