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Proteins that recognize the conserved cis-acting sequences of RNA viruses

Is the cognate protein(s) of viral or host origin?

Minus strand viruses

Virions of minus-strand and double-strand RNA viruses necessarily package the enzyme activities for the production of mRNA transcripts required for initiating infection.

• Purified, detergent-disrupted virions of VSV [Benarjee, 1987] and influenza virus [Plotch and Krug, 1977] are long known to be capable of producing the primary transcripts.
  For these viruses, host factors probably have little or no role in the recognition of the cis-acting sequences for primary transcription. However, it is still possible that they participate in recognizing the cis-acting sequences for subsequent replication steps.
• Synthesis of full-length dsRNA has been observed with purified rotavirus open core particles supplied with exogenous, full-length plus-strand templates [Chen et al., 1994].
  It is unlikely that host factors play any role in recognizing the relevant cis-acting sequence in this system.

Plus strand viruses

Cognate proteins could be either viral and/or host
• Evidence for a role for host proteins
  • Although binding of cis-acting sequences per se does not necessarily imply functional significance, the evidence indirectly suggest a role for the host factors. For example,
    
    • Binding of host factors to the cis-acting sequences of Togaviruses [Pardigon and Strauss, 1992; Pardigon et al., 1993; Pardigon and Strauss. 1996; Nakhasi et al., 1990; Nakhasi et al., 1991].

  • As components of the replication complex. For example:
    
    • Host factors associated with RNA phage replicases [Van Duin, 1988]. Evidence for the ribosomal protein S1, as part of the replicase, binding to a cis-acting sequence regulating translation versus minus-strand synthesis [Kolakofsky and Weissmann, 1971; Goelz and Steitz, 1977].
    • Host factor associated with the cucumber mosaic virus replicase [Hayes and Buck. 1990].
    • Host factor associated with the poliovirus replicase [Dasgupta et al., 1980; Baron and Baltimore, 1982].

• Evidence for a role for viral replicases
  • There is abundant evidence that viral replication proteins are required for viral RNA synthesis. In most systems, however, it is not clear if the viral proteins bind to and recognize the conserved cis-acting sequences.
  • A functional ribonucleoprotein complex, containing both viral and host proteins, forms at the conserved 5' end cloverleaf of poliovirus RNA [Andino et al., 1990]

Those that are not available through PubMed of the National Library of Medicine, USA.

• Van Duin, J. 1988. Single-stranded RNA bacteriophages, p. 117-167. In R. Calender (ed.), The Bacteriophages. Plenum Press, New York.