Rubella virus RNA replication is cis-preferential and synthesis of negative- and positive-strand RNAs is regulated by the processing of nonstructuralprotein

Rubella virus (RV) genome encodes nonstructural protein (NSP) in a large op en reading frame at its 5 ' end. It is translated into p200 and further pro cessed into p150 and p90. The NSPs are responsible for viral RNA replicatio n, during which a full-length negative-strand RNA serves as the intermediat e for the replication of positive-strand genomic RNA and the transcription of subgenomic RNA. Using complementation experiments, we demonstrated that RV negative-strand RNA is synthesized preferentially in cia while positive- strand RNAs can be synthesized both in cis and in trans but with higher eff iciency in cis. During virus infection, negative-strand RNA accumulates unt il 10 hours postinfection (hpi) acid remains nearly constant thereafter. In contrast, positive-strand RNAs (both genomic and subgenomic RNA) do not in crease much before 10 hpi and accumulate rapidly thereafter. Previously we demonstrated that p200 synthesizes negative- but not positive-strand RNA, w hereas cleavage products p150/p90 are required for efficient production of positive-strand RNAs. In this study, we present evidence demonstrating that a higher concentration of p150/p90 is associated with lower production of negative-strand RNA. Our data support the hypothesis that p200 is the princ ipal replicase for negative-strand RNA, as is p150/p90 for positive-strand RNA. The switch from the synthesis of negative- to positive-strand RNA is t hus regulated by NSP processing, which not only activates the efficient pro duction of positive-strand RNA, but also disables negative-strand RNA synth esis. A mechanism for NSP translation, processing, and regulation of RV RNA synthesis is proposed. (C) 2001 Academic Press.