The return of the "Mistigri" (virus adaptative gain by gene loss) through the SARS-CoV-2 XBB.1.5 chimera that predominated in 2023.

ABSTRACT

Severe acute respiratory syndrome coronavirus 2 XBB.1.5 is the first recombinant lineage to predominate at the country and global scales. Very interestingly, like the Marseille-4B subvariant (or B.1.160) and the pandemic variant B.1.1.7 (or Alpha) previously, it has its ORF8 gene inactivated by a stop codon. We aimed here to study the distribution of stop codons in ORF8 of XBB.1.5 and non-XBB.1.5 genomes. We identified that a stop codon was present at 89 (74%) ORF8 codons in ≥1 of 15 222 404 genomes available in GISAID. The mean proportion of genomes with a stop codon per codon was 0.11% (range, 0%-7.8%). In addition, a stop codon was detected at 15 (12%) codons in at least 1000 genomes. These 15 codons are notably located on seven stem-loop hairpin regions and in the signal peptide region for the case of the XBB.1.5 lineage (codon 8). Thus, it is very likely that stop codons in ORF8 gene contributed on at least three occasions and independently during the pandemic to the evolutionary success of a lineage that became transiently predominant. Such association of gene loss with evolutionary success, which suits the recently described Mistigri rule, is an important biological phenomenon very unknown in virology while largely described in cellular organisms.