MSH3 Homology and Potential Recombination Link to SARS-CoV-2 Furin Cleavage Site

Abstract

Among numerous point mutation differences between the SARS-CoV-2 and the bat RaTG13 coronavirus, only the 12-nucleotide furin cleavage site (FCS) exceeds 3 nucleotides. A BLAST search revealed that a 19 nucleotide portion of the SARS.Cov2 genome encompassing the furing cleavage site is a 100% complementary match to a codon-optimized proprietary sequence that is the reverse complement of the human mutS homolog (MSH3). The reverse complement sequence present in SARS-CoV-2 may occur randomly but other possibilities must be considered. Recombination in an intermediate host is an unlikely explanation. Single stranded RNA viruses such as SARS-CoV-2 utilize negative strand RNA templates in infected cells, which might lead through copy choice recombination with a negative sense SARS-CoV-2 RNA to the integration of the MSH3 negative strand, including the FCS, into the viral genome. In any case, the presence of the 19-nucleotide long RNA sequence including the FCS with 100% identity to the reverse complement of the MSH3 mRNA is highly unusual and requires further investigations.

Keywords: MSH3 gene; SARS-CoV-2 spike; furin cleavage site; recombinability; sequence homology.

FIGURE 1 |

The origin of the furin sequence in SARS-CoV-2. Comparison of the protein sequences at the S1/S2 junction in SARS-CoV, RaTG13, and SARS-CoV-2 demonstrating the presence of the furin cleavage site (FCS) PRRA only in SARS-CoV-2. Based on a BLAST search of the 12-nucleotide stretch coding for the FCS PRRA, a 19-nucleotide long identical sequence was identified in the patented (US 958 7003) sequence Seq ID11652. SEQ ID11652 is transcribed to a MSH3 mRNA that appears to be codon optimized for humans. This 19-nucleotide sequence including 12 nucleotides coding for the FCS PRRA, present in the human MSH3 gene might have been introduced into the SARS-CoV-2 genome by the illustrated copy choice recombination mechanism in SARS-CoV-2 infected human cells overexpressing the MSH3 gene.

FIGURE 2 |

Calculations of the probability of natural occurrence of the 19nt sequence under study. The SARS-CoV-2 genome is ∼30,000 nucleotides long (P1). The patented sequence is ∼3,300 nucleotides long (P2). The patented library encompasses 24’712 sequences of varying lengths with median length being in the range of 3,300 nucleotides. Conventional probability calculations are given of the probability of the presence of a 19-nucleotide sequence in the human genome and in one of the patented library sequences.