SARS Accessory Proteins ORF3a and 9b and Their Functional Analysis

The SARS coronavirus (CoV) positive-stranded RNA viral genome encodes 14 open reading frames (ORFs), eight of which encode proteins termed as “accessory proteins.” These proteins help the virus infect the host and promote virulence. In this chapter we describe some of our latest investigations into the structure and function of two such accessory proteins: ORF3a and 9b. The ORF3a accessory protein is the largest accessory protein in SARS-CoV and is a unique membrane protein consisting of three transmembrane domains. It colocalizes on the cell membrane and host Golgi networks and may be involved in ion channel formation during infection. Similarly the ORF9b accessory protein is 98 amino acids, associates with the spike and nucleocapsid proteins and has unusual membrane binding properties. In this chapter we have suggested possible new roles for these two accessory proteins which may in the long run contain answers to many unanswered questions and also give us new ideas for drugs and vaccine design.