The impact of genome length on replication and genome stability was assessed for guinea pig cytomegalovirus (GPCMV), a member of the Herpesviridae. The 233-kb genome could be decreased by 15.1 kb without discernable impact on viral replication efficiency in vitro. Viruses with genomes under-length by up to 31 kb replicated with decreased efficiencies but this appeared to arise from the loss of augmenting viral genes rather than decreased genome length. Two deletions that were non-lethal on their own were lethal when combined, suggesting that the resulting 40.1 kb under-length genome fell below a minimum packageable size. Genomes over-length by 8.8 kb gave rise to spontaneous deletions just to the right of the major immediate early locus, the same region that undergoes deletions during fibroblast passage of human and rhesus cytomegaloviruses. These results suggest that genome integrity should be confirmed for herpesvirus mutants in which genome length is increased even modestly.
Bibliographical noteFunding Information:
The authors are grateful to Gabriele Hahn and Wolfram Brune for providing pCre, Dong Yu for providing pYD-Tn1721, and Greg Smith for providing pGS284 and E. coli strain GS500. This work was supported by a grant R01HD044864 from the National Institutes of Health.
- Genome length
- Genome maturation