The three faces of riboviral spontaneous mutation: spectrum, mode of genome replication, and mutation rate

Tuesday, October 09, 2012 — Poster Session I
1:00 p.m. – 3:00 p.m	Natcher Conference Center, Building 45	NIEHS	VIROL-6

Authors

• L. García-Villada
• J.W. Drake

Abstract

Riboviruses are the most abundant pathogens infecting animals and plants. Few riboviral infections can be controlled with antiviral drugs, mainly because of the appearance of resistance mutations. Yet, little information is available concerning i) kinds of mutations (the mutational spectrum), ii) mode of genome replication, and iii) rates of spontaneous mutation. To illuminate these issues, we developed a model system based on phage Qß infecting its natural host, Escherichia coli. The Qß RT gene was used as mutation reporter. Selection against RT mutants during phage growth was ameliorated by plasmid-based complementation in trans. A total of 32 RT mutants were detected among 7517 Qß isolates. Sequencing analysis of 45 RT mutations revealed a spectrum dominated by 39 transitions, plus 4 transversions and 2 indels. The dynamics of Qß genome replication were confirmed to reflect the linear process of iterative copying. The estimated mutation rate per genome replication was ≈ 0.04 (or ≈ 0.08 per phage generation), although secondary RT mutations arose at a rate about 7-fold higher, signaling the possible impact of transitory bouts of hypermutation. These results are contrasted with those previously reported for other riboviruses to depict the current state of the art in riboviral mutagenesis.

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