Recombination and polymerase error facilitate restoration of infectivity in brome mosaic virus

• Published in: Journal of Virology 1993-02, Vol.67 (2), p.969-979
• Main Authors: Rao, A.L.N. (Texas AandM University, College Station, TX), Hall, T.C
• Format: Article
• Language: English
• Subjects: ARN; Base Sequence; Biological and medical sciences; brome mosaic virus; BROMOVIRUS; CHENOPODIUM; Fundamental and applied biological sciences. Psychology; Gene Expression; Genetic Variation; Genetics; GENOMAS; GENOME; Genome, Viral; Hordeum - drug effects; Hordeum - microbiology; HORDEUM VULGARE; Microbiology; Models, Molecular; Molecular Sequence Data; Mosaic Viruses - genetics; Mosaic Viruses - growth & development; Mosaic Viruses - pathogenicity; MUTACION INDUCIDA; Mutagenesis; MUTANT; MUTANTES; MUTATION PROVOQUEE; Nucleic Acid Conformation; Plants - drug effects; Plants - microbiology; PODER PATOGENO; POUVOIR PATHOGENE; Protoplasts - microbiology; RECOMBINACION; RECOMBINAISON; Recombination, Genetic; Regulatory Sequences, Nucleic Acid - genetics; RNA Replicase - metabolism; RNA, Viral - pharmacology; SECUENCIA NUCLEICA; SEQUENCE NUCLEIQUE; TRANSFERASAS; TRANSFERASE; Virology; VIRUS DE LAS PLANTAS; VIRUS DES VEGETAUX; Virus Replication
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.67.2.969-979.1993

The tRNA-like structure present in the 3' noncoding region of each of the four virion RNAs of brome mosaic virus possesses a conserved A-67-U-A-65 ((67)AUA(65)) sequence. Four mutations in this region ((67)UAA(65), (67)GAA(65), and (67)CAA(65), each with a double base change, and (67)GUA(65), containing a single point mutation), previously shown in vitro to be defective in minus-strand promoter function, were introduced into full-length genomic RNAs 2 and 3, and their replicative competence was analyzed in barley protoplasts. All four RNA 3 mutants were capable of replication, although progeny plus-sense RNA 3 accumulation was only 12 to 42% of that of the wild type. Replication of RNA 2 transcripts bearing these mutations was even more severely debilitated; the accumulation of each mutant progeny plus-strand RNA 2 was 10% of that of the wild type. Analysis of mutant RNA 3 progeny recovered from local lesions induced in Chenopodium hybridum and systemic infections in barley (Hordeum vulgare) plants revealed that the mutant base at position 67 from the 3' end had in each case been modified to an A. These changes generated RNAs with functional pseudorevertant ((67)AAA(65) for mutants (67)UAA(65), (67)GAA(65), and (67)CAA(65)) or revertant ((67)GUA replaced by (67)AUA(65)) sequences. In most instances, the presence of internal markers permitted discrimination between polymerase error and RNA recombination as the process by which sequence restoration occurred. The pseudorevertant sequence was found to be capable of persistence during subsequent propagation in plants when present on RNA 3 but not when present on RNA 2. These data document the fluidity of the RNA genome and reveal situations in which polymerase error or recombination can function preferentially to restore an optimal sequence. They also support the concept that RNA viruses frequently exist as quasispecies and have implications concerning evolutionary strategies for positive-strand RNA viruses