REPLICATION OF A PLANT-VIRUS SATELLITE RNA - EVIDENCE FAVORS TRANSCRIPTION OF CIRCULAR TEMPLATES OF BOTH POLARITIES

The sequences of sTobRV RNA and other small satellite RNAs appear to be neither transcribed into DNA nor translated into protein. Replication and the other activities, such as influence over supporting virus-induced symptom development, seem to require satellite sequences only in the form of RNA of both polarities. A model for the replication of sTobRV RNA employs circular RNAs both of the abundant polarity and of the less abundant polarity (sTobRV [-] RNA) as templates for the synthesis of complementary, multimeric RNA. In this model, processing of the multimeric RNA generates the respective unit-length, monomeric sTobRV RNA, completing the replication cycle. Evidence in favor of this model, which is qualitatively symmetric with regard to the participation of each polarity of RNA, includes the discovery of 1) circular and multimeric forms of both polarities of sTobRV RNA, 2) autolytic processing of both polarities of multimeric sTobRV RNA in vitro, and 3) an association, in a set of sTobRV RNA mutants, of the ability to initiate replication and the ability, of sTobRV (-) RNA, to circularize spontaneously in vitro.