Brome mosaic, bromoviruses


Ahlquist, P. Bromovirus RNA replication and transcription. Curr. Opinion in Genetics & Dev. 2, 21-76 (1992)
Ahlquist, P. Bromoviruses in Encyclopedia of Virology, 2nd edition (1999)
Ahlquist, P., French, R. and Buzarski, J.J. Molecular studies of brome mosaic virus using infectious transcripts from cloned cDNA. Advan. Virus Res. 32, 215-42 (1987)
Bol, J.F. Alfalfa mosaic virus: coat protein-dependent initiation of infection, Mol. Plant Pathology 4, 1 2003
De Jong, W., Ahlquist, P. Bromovirus specificity and systemic infection. Sem. in Virol. 2, 97-105 (1991)
De Jong, W., Chu, A., and Ahlquist, P. Coding changes in the 3a cell-to-cell movement gene can extend the host range of brome mosaic virus systemic infection. Virol. 214, 464- 74 (1995)
Noueiry A.O., Ahlquist, P. Brome Mosaic Virus RNA Replication: Revealing the Role of the Host in RNA Virus Replication. Ann. Rev. Phytopath. 41, 77-98 (2003)
Ding, S-W., Shi, B-J., Li, W-X., Symons, R.H. An interspecies hybrid RNA virus is significantly more virulent than either parental virus. PNAS 93, 7470-74 (1996)
Kao, C.C., Sivakumaran, K. Brome mosaic virus, Good for and RNA virologists basic needs. Mol. Plant Pathology 1, 91-97, 2000
Van Rossum, C.M.A., Neeleman, L., Bol, J.F. Comparison of the role of the 5' terminal sequences of alfalfa mosaic virus RNAs 1,2, and 3 in viral RNA replication. Virol. 235, 333-41 (1997)


Bromoviruses (brome mosaic - BMV, cowpea chlorotic mottle - CCMV, broad bean mottle - BBMV)

1- Physical properties
a- Single 86S component in the ultracentrifuge
b- 4.5Md and about 23% RNA
c- Early studies showed that virions contained 1.0, 0.7 and 0.3Md RNAs
d- Suggested infectious RNA plus 2/3, 1/3 fragments (specific cleavage model)
2- Higher resolution studies on RNA
a- Gel electrophoresis shows 4 RNAs (1.1Md, 1.0Md, 0.7Md, 0.3Md)
b- Virions heterogeneous by buoyant density (virions have different RNA contents)
c- Analysis of RNA in density fractions shows three classes of virions
d- Heavy virions have 1.1Md RNA, light virions have 1.0Md RNA, intermediate density virions have two smaller RNAs in equimolar ratio
e- Deleting any of the largest 3 RNAs from a mix of 4 greatly reduces infectivity
f- All 4 RNAs charged by tyrosine-tRNA ligases (similar 3' ends)
g- All RNAs are capped with 7-meG
3- Genetics
a- RNA component mixing experiments show that RNA3 (0.7Md) encodes cp
b- RNA sequencing shows that RNA4 is cp mRNA
c- Mix of RNA1 and RNA2 replicates in isolated protoplasts
d- Sequencing - RNA1 & 2 encode replicase, RNA3 encodes movement (mp) and cp.
e- Bromovirus genes resemble TMV genes (dot matrix comparision) - alphaviruses)
4- Studies with infectious transcripts
a- Paul Ahlquist first makes infectious transcripts (T7 RNA polymerase)
b- 7-MeG cap important with as little "extra" sequence as possible
c- Virus with deleted mp gene multiplies normally in protoplasts (but not in plants)
d- Roy French shows that intergenic promoter of RNA3 essential for its replication
e- Virus multiplies with CCMV cp gene substituted for BMV cp gene
f- BMV-CCMV chimeras with exchanged mp infect N. benthamiana but not native hosts
5- BMV polymerase
a- Get template dependent enzyme by digesting with S1 nuclease, adding EGTA
b- RNA3 minus strand an effective template for making RNA4
c- tRNA-like structures essential to use (+) strands as templates
d- Host protein synthesis initiation factor associated with BMV polymerase
e- Polymerase proteins (1a, 2a) interact bly with one another
f- Polymerase tightly associated with endoplasmic reticulum