Disease relevance of 3a

• Cucumber mosaic virus 2a polymerase and 3a movement proteins independently affect both virus movement and the timing of symptom development in zucchini squash [1].
• The 3a movement protein (MP) of a plant virus, Cucumber mosaic virus (CMV), forms ribonucleoprotein (RNP) complexes with viral RNA, capable of trafficking from cell-to-cell throughout the infected plant only in the presence of the CMV capsid protein (CP) [2].
• The soluble, His-tagged 3a proteins, affinity-purified from E. coli and zucchini squash, both were able bind CMV RNA 3 in vitro [3].
• The cucumber mosaic virus (CMV) 3a movement protein (MP) was compared directly to the well-characterized tobacco mosaic virus (TMV) 30K MP by cloning the genes encoding these proteins into Escherichia coli, isolating the E. coli-expressed MPs, and characterizing them with regard to RNA- and NTP-binding activities [3].

High impact information on 3a

• We obtained mutants containing mutations in the two open reading frames in CMV RNA3 encoding the 3a protein and the capsid protein (CP), both of which are necessary for cell-to-cell movement of CMV [4].
• A C-terminal deletion in CMV 3a (3a Delta C33) abolished the requirement of CP in transporting the ToMV genome [5].
• These data indicate that viral movement out of the initially infected epidermal cell, and not the simultaneous expression in this cell of the 3a protein and the CP, is required for the induction of cell death [6].
• cDNA clones of cucumber mosaic virus (CMV) RNA 3 were modified to express the jellyfish green fluorescent protein (GFP) in place of the 3a movement protein (MP) or coat protein (CP), as fusions to the N (GFP-3a) or C (3a-GFP) terminus of the MP or from a separate open reading frame as part of tricistronic RNAs 3 [7].
• PSV 3a and CP genes have higher percentage nucleotide sequence identities to those of tomato aspermy cucumovirus than to those of CMV [8].

Chemical compound and disease context of 3a

• The CMV 3a protein expressed either in E. coli or in planta from RNA 3 of CMV was tagged at its C-terminus with six histidine residues, which facilitated its purification by affinity chromatography on a matrix containing Ni(2+)-nitrilotriacetate [3].

Biological context of 3a

• Both RNAs contain two open reading frames, the 3a gene and the coat protein gene [9].
• Sequence analysis of the 3a gene of Sny-CMV showed that there were three nucleotide changes that altered amino acid sequences within the MP [10].
• In the present study, the nucleotide sequences of the 3a and CP genes of SSV were determined, and the data were used to classify seven SSV isolates among known Cucumber mosaic virus (CMV) strains [11].
• These same sequence changes previously were shown to be associated with high levels of 3a protein accumulation and chronic vs acute, cyclic infection typical of Sny-CMV vs Fny-CMV [Gal-on et al. (1996). Virology 226, 354-361] [12].
• By analogy to other tripartite plant viruses, it is presumed that the first ORF (867 nucleotides) codes for the 3a protein and the second ORF (654 nucleotides) is the cistron of the coat protein which is expressed from subgenomic RNA 4 of 1010 nt residues [13].

Anatomical context of 3a

• In both cases, considerably more 3a protein was associated with a fraction containing membranes [10].
• Comparative analyses of seven mutated 3a proteins obtained from inclusion bodies and eight GST fusion proteins revealed that there is an RNA-binding domain located between amino acids 174 and 233 [14].
• Dye-coupling experiments using fluorescent-dextran probes were performed on fully expanded leaves to study the modifying effect of CMV 3a protein on the gating capacity of plasmodesmata [15].
• Mutation of the 3a protein had no effect on RNA3 accumulation in protoplasts, whereas CP mutations caused reduced CMV RNA accumulation [16].
• The 3a protein was predominantly localized in a subcellular fraction corresponding to the cytosol [17].

Other interactions of 3a

• Complementation experiments with mutant CMV RNA3 showed that only 3a protein mutants, i.e., those with an intact CP, complemented the long-distance movement of 1-TAV in cucumbers [4].

Analytical, diagnostic and therapeutic context of 3a

• Deletions in the 3a gene were generated by PCR and restriction digestion, and the resulting mutated 3a sequences were cloned either in pT7-7 or in pGEX-5X3 expression vectors [14].
• These data were corroborated by immunocytochemistry performed in both infected and 3a-expressing transgenic tobacco plants [18].
• Microinjection studies performed on transgenic tobacco plants expressing the CMV 3a protein indicated that fluorescently labeled CMV RNA moved out of the target cell into the surrounding mesophyll tissue [19].
• Probing the MP-RNA complexes by atomic force microscopy demonstrated that the ORF4-encoded protein bound RNA incompletely, leaving protein-free RNA segments of varying length, while the CMV 3a protein formed highly packed complexes [20].

References