Barbara Weiss

Defective RNAs of Alphaviruses

Most viruses, when passaged at high multiplicity in cultured cells, accumulate deletion mutants characterized by their ability to interfere with the replication of the standard virus. These mutants are defined as defective interfering (DI) particles (Huang and Baltimore, 1970; Perrault, 1981). One of their hallmarks is the specificity of their inhibition; they interfere only with the replication of homologous or closely related viruses. Why study DI particles? What can they tell us about the standard virus or about virus—host interactions? The following points attempt to answer these questions and provide the framework for this chapter.

Formation of RNA and protein in cells infected with standard and defective Sindbis virus

Our studies on the formation of Sindbis virus proteins have established that: 1. one of the two envelope proteins (E2) accumulates in infected cells as a higher molecular weight precursor that is slowly converted to the virion protein; 2. the large protein (mol. wt ≧ 130000 daltons), that accumulates in cells infected with a temperature-sensitive mutant of Sindbis virus contains sequences of the three virion proteins; and 3. the protein (mol. wt. ≧ 100000 daltons) isolated from BHK cells infected with Sindbis virus is related in sequence to the two envelope proteins.We have investigated the formation of defective-interfering (DI) particles of Sindbis virus and their ability to inhibit the replication of standard virus. BHK cells infected with passages of Sindbis virus containing DI particles accumulate a species of RNA (20S) that is about half the molecular weight of the 26S RNA. We have demonstrated by competitive hybridization experiments that 20S RNA contains half the sequences of 26S RNA. We also present evidence that in contrast to 26S RNA, 20S does not bind to polysomesin vivo and is not translatedin vitro.