Characterization of the TMV encapsidation initiation site on 18S rRNA

Replication of Plant Viruses

Viruses replicate using both their own genetic information and host cell components and machinery. The different genome types have different replication pathways which contain controls on linking the process with translation and movement around the cell as well as not compromising the infected cell. This chapter discusses the replication mechanisms, faults in replication and replication of viruses co-infecting cells.

Viruses replicate using both their own genetic information and host cell components and machinery. The different genome types have different replication pathways which contain controls on linking the process with translation and movement around the cell as well as not compromising the infected cell. This chapter discusses the replication mechanisms, faults in replication and replication of viruses coinfecting cells.

Study of TMV assembly with heterologous RNA containing the origin-of-assembly sequence

The assembly of tobacco mosaic virus (TMV) is initiated by a specific reaction between a capsid protein oligomer and an origin-of-assembly region (OAS) located 900 nucleotides from the 3' terminus of virion RNA. Packaging is then completed by rod elongation both in the 5' and 3' directions. The temporal order of the direction of elongation and the characteristics of the reaction were studied by analysis of the in vitro assembly reaction between strain U1 protein oligomers and transcripts containing a strain U1 OAS embedded at different positions in heterologous RNA. The results confirm that elongation in the 5' direction starts very soon after the initiation reaction and is completed rapidly, within minutes. Packaging in the 3' direction is slower and does not appear to commence until 5' rod formation is complete. The reaction of strain U2 protein with the strain U1 OAS initiates rapidly, but elongation occurs only in the 5' direction; 3' packaging does not occur except when the OAS is at or near the 5' terminus, in which case elongation in the 3' direction initiates without delay with either the U1 or U2 protein. Pauses occur during elongation in the 3' direction at an average of 320 nucleotides, indicating a packaging periodicity of about six to eight helical turns.

Localization of multiple TMV encapsidation initiation sites on rbcL gene transcripts

TMV capsid protein reacts with and encapsidates many of the chloroplast DNA transcripts both in vivo and in vitro to form pseudovirions. We report on the encapsidation initiation reaction with one of the major RNA species found in in vivo formed pseudovirions, the mRNA for the chloroplast-encoded large subunit of ribulose bisphosphate carboxylase/oxygenase (rbcL). This mRNA is found to contain at least three sites which are independently capable of reacting with capsid protein oligomers to initiate encapsidation. All three sites react with capsid protein less efficiently in vitro than does the functional viral RNA encapsidation initiation site (ei). The 5' portion of the region that contains the most reactive rbcL site, ei-3, shows significant nucleotide sequence homology with the encapsidation initiation sites of the U1 and Cc strains of TMV and it can assume a folding structure that resembles that postulated for the Cc strain site. A site that acts as a block to rod elongation is present in transcripts from the region just 3' to the segment from which the rbcL mRNA is transcribed, probably close to, or at the transcription termination signal.