Generation of a novel SARS-CoV-2 sub-genomic RNA due to the R203K/G204R variant in nucleocapsid

The adjacent amino acid polymorphisms in the nucleocapsid (R203K/G204R) of SARS-CoV-2 arose on the background of the spike D614G change and strains harboring these changes have become dominant circulating strains globally. Sequence analysis suggests that the three adjacent nucleotide changes that result in the K203/R204 variant have arisen by homologous recombination from the core sequence (CS) of the leader transcription-regulating sequence (TRS) as opposed to a step-wise mutation model.

The resulting sequence changes generate a novel sub-genomic RNA transcript for the C-terminal dimerization domain. Deep sequencing data from 981 clinical samples confirmed the presence of the novel TRS-CS-dimerization domain RNA in individuals with the K203/R204 variant. Quantification of sub-genomic RNA indicates that viruses with the K203/R204 variant may also have increased expression of sub-genomic RNA from other open reading frames. The K203/R204 variant results in a novel sub-genomic RNA.

The finding that homologous recombination from the TRS may have occurred since the introduction of SARS-CoV-2 in humans resulting in both coding changes and novel sub-genomic RNA transcripts suggests this as a mechanism for diversification and adaptation within its new host.