Replication and translation of cowpea mosaic virus RNAs are tightly linked.
The genome of cowpea mosaic virus (CPMV) is divided among two positive strand RNA molecules. B-RNA is able to replicate independently from M-RNA in cowpea protoplasts. Replication of mutant B-transcripts could not be supported by co-inoculated wild-type B-RNA, indicating that B-RNA cannot be efficiently replicated in trans. Hence replication of a B-RNA molecule is tightly linked to its translation and/or at least one of the replicative proteins functions in cis only. Remarkably also for efficient replication of M-RNA one of its translation products was found to be required in cis. This 58K protein possibly helps in directing the B-RNA-encoded replication complex to the M-RNA. In order to identify the viral polymerase the CPMV B-RNA-specific proteins have been produced individually in cowpea protoplasts using CaMV 35S promoter based expression vectors. Only protoplasts transfected with a vector containing the 200K coding sequence were able to support replication of co-transfected M-RNA. Despite this, CPMV-specific RNA polymerase activity could not be detected in extracts of these protoplasts using a poly(A)/oligo(U) assay. These results indicate that, in contrast to the poliovirus polymerase, the CPMV polymerase is not able to accept oligo(U) as a primer and in addition support the concept that translation and replication are linked.
Wellink
J
J
Department of Molecular Biology, Agricultural University, Wageningen, The Netherlands.
van Bokhoven
H
H
Le Gall
O
O
Verver
J
J
van Kammen
A
A
D000818:Animals; D002478:Cells, Cultured; D017798:Comovirus / Q000235:genetics / Q000254:growth & development*; D004252:DNA Mutational Analysis; D012321:DNA-Directed RNA Polymerases / Q000096:biosynthesis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology; D007313:Insecta / Q000166:cytology; D008957:Models, Genetic; D010946:Plants, Medicinal; D014176:Protein Biosynthesis; D011523:Protoplasts / Q000382:microbiology; D012367:RNA, Viral / Q000096:biosynthesis* / Q000235:genetics; D014779:Virus Replication
D012367:RNA, Viral; D012321:DNA-Directed RNA Polymerases