Extreme Mutation Tolerance: Nearly Half of the Archaeal Fusellovirus Sulfolobus Spindle-Shaped Virus 1 Genes Are Not Required for Virus Function, Including the Minor Capsid Protein Genevp3.
Viruses infecting theArchaeaharbor a tremendous amount of genetic diversity. This is especially true for the spindle-shaped viruses of the familyFuselloviridae, where >90% of the viral genes do not have detectable homologs in public databases. This significantly limits our ability to elucidate the role of viral proteins in the infection cycle. To address this, we have developed genetic techniques to study the well-characterized fusellovirus Sulfolobus spindle-shaped virus 1 (SSV1), which infectsSulfolobus solfataricusin volcanic hot springs at 80°C and pH 3. Here, we present a new comparative genome analysis and a thorough genetic analysis of SSV1 using both specific and random mutagenesis and thereby generate mutations in all open reading frames. We demonstrate that almost half of the SSV1 genes are not essential for infectivity, and the requirement for a particular gene correlates well with its degree of conservation within theFuselloviridaeThe major capsid genevp1is essential for SSV1 infectivity. However, the universally conserved minor capsid genevp3could be deleted without a loss in infectivity and results in virions with abnormal morphology.IMPORTANCEMost of the putative genes in the spindle-shaped archaeal hyperthermophile fuselloviruses have no sequences that are clearly similar to characterized genes. In order to determine which of these SSV genes are important for function, we disrupted all of the putative genes in the prototypical fusellovirus, SSV1. Surprisingly, about half of the genes could be disrupted without destroying virus function. Even deletions of one of the known structural protein genes that is present in all known fuselloviruses,vp3, allows the production of infectious viruses. However, viruses lackingvp3have abnormal shapes, indicating that thevp3gene is important for virus structure. Identification of essential genes will allow focused research on minimal SSV genomes and further understanding of the structure of these unique, ubiquitous, and extremely stable archaeal viruses.
Center for Life in Extreme Environments and Biology Department, Portland State University, Portland, Oregon, USA.
Eric A
EA
Iverson
Center for Life in Extreme Environments and Biology Department, Portland State University, Portland, Oregon, USA.
David A
DA
Goodman
Center for Life in Extreme Environments and Biology Department, Portland State University, Portland, Oregon, USA.
Madeline E
ME
Gorchels
Center for Life in Extreme Environments and Biology Department, Portland State University, Portland, Oregon, USA kstedman@pdx.edu.
Kenneth M
http://orcid.org/0000-0001-6086-0238
KM
Stedman
D036022:Capsid Proteins / Q000235:genetics*; D019241:Fuselloviridae / Q000235:genetics* / Q000378:metabolism; D016679:Genome, Viral; D045482:Hot Springs; D009154:Mutation; D016944:Sulfolobus / Q000235:genetics / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014771:Virion / Q000235:genetics; D019065:Virus Assembly
D036022:Capsid Proteins; D014764:Viral Proteins
Archaea; morphogenesis; mutational studies; virus assembly