Viruses act in host cells by reproducing their own proteins for reconstituting their capsid, duplicating their genome [1] and leaving non-coding RNA or DNA remnants in host genomes [2] .
Moreover, RNA viruses can also form complexes with existing mRNAs and/or proteins of host cells.
Thereby they might prevent protein function, behave like microRNAs [3] [4] [5] [6] or ribosomal RNAs [6] [7] [8] , inhibiting or favoring the translation of specific proteins of host cells [9] [10] [11] [12] [13] [14] [15] [16] [17] . If these proteins are vital for the host, viral pathogenicity is much greater than that caused by viral replication. With regard to SARS-CoV-2, binding to existing host proteins has already been described [18] . Here, we aim to describe a potential miRNA-like action by viral RNA, in particular i) at the level of oxygen transport by hemoglobin, whose beta-globin and gamma 2 subunits synthesis can be inhibited, and ii) at the level of immune response, where type I interferon synthesis can be inhibited. We are not intending to prove here experimentally these inhibitions by small RNAs issued from the SARS-CoV-2 genome, but to prepare this future empirical step by pointing out its potential hybridizing power. In Section 2, we describe a method for finding SARS-CoV-2 inhibitory RNA sub-sequences, and results are given in Section 3, we discussed in Section 4. Some perspectives of this work concerning an extension to the inhibition of translation of olfactory and interferon receptors are proposed in Section 5.
Focusing on the seed part of miRNA-like sequences having a putative 8 nucleotide hybridization seed inhibition effect [19] [20] (minimum 7), we compare data from different databases [21] [22] [23] [24] [25] [26] using BLAST [27] . Figure 1 shows microRNA 129-5p, a known inhibitor of a human foetal hemoglobin component, the gamma-globin 2, replaced in adult by the beta-globin regulated as the other component alpha-globin, by microRNAS [28] [29] [30] [31] [32] . Two sub-sequences from the SARS-CoV-2 genome, namely from genes of ORF10 and protein S, show the same hybridizing potential. [22] . Sequences in green (resp. red) come from protein S and ORF10 genes of SARS-CoV-2 (resp. hsa miR 129-5p), which can inhibit its ribosomal translation. Probability of length 8 anti-match in red (resp. 9 and 11 in green) by chance in 577 nucleotides equals 0.035 (resp. 0.017 and 0.0003) (T-G and G-T matches counting for ½).
We will apply the method from Section 2 for showing examples where RNA subsequences of the SARS-CoV-2 genome have an inhibitory potential on the ribosomal translation of human mRNAs of the same type as that shown in Section 2 for human micro-RNAs. For example, miRTarBase shows that microRNA hsa-mir-92a-3p targets the beta-globin HBB subunit of adult hemoglobin, inhibiting its translation [25] . This is also the case for microRNas involved in the maturation of erythrocytes like miR-451a [26] [27] [28] [29] [30] [31] . We exhibit on Figure 2 subsequences of the SARS-CoV-2 protein S and polymerase genes [23] having the same length of antimatching as these microRNAs on the mRNA of the hemoglobin beta-globin (HBB) subunit gene. Human beta-globin gene [24] potentially targeted by a subsequence of the gene of the SARS-CoV-2 RNA-dependent RNA polymerase (in blue) and by a subsequence of the gene of the SARS-CoV-2 protein S (in green) [23] , by the human microRNAs hsa miR 92a-3p (in red) and hsa miR 451a (in red). Probability of red anti-matches of length 8 in a sequence of 624 nucleotides equals 0.04 and for the blue (resp. green) subsequence is 0.005 (resp. 0.017) (T-G and G-T matches counting for ½).
The second example concerns the gene of the spicule protein S of SARS-CoV-2, which shares a long subsequence of length 14 (664-678) with the gene of the Gag protein of the virus HERV-K102 ( Figure 3 ). Its potential targets are the mRNAs of human hemoglobin subunit beta-globin [22] , human hemoglobin subunit gamma-globin 2 (HBG2) [23] , human type 1 interferons and the human receptor ACE2. [27] . The second of length 23 (1112-1134) anti-matches a mRNA subsequence of hemoglobin subunit beta-globin [22] .
The third of length 22 (1200-1221) anti-matches a mRNA subsequence of hemoglobin subunit gamma-globin 2 (HBG2) [23] . The fourth of length 24 (2032-2055) matches a subsequence of mRNA of many type 1 interferons. Highlighted in yellow are sub-sequences common with the SARS furin cleavage site [33] [34] . The fifth of length 25 (3152-3176) matches a subsequence of mRNA of the receptor ACE2. Blue: mutations whose location of both codon and nucleotide involved [35] TCTTCAGCAAAATGGGTCTTCAGTGCTCTCAGAAGACAAGAGCAAACGGTTGAACACAATTCTAAATACA  ATGAGCACCATCTACAGTACTGGAAAAGTTTGTAACCCAGATAATCCACAAGAATGCTTATTACTTGAAC  CAGGTTTGAATGAAATAATGGCAAACAGTTTAGACTACAATGAGAGGCTCTGGGCTTGGGAAAGCTGGAG  ATCTGAGGTCGGCAAGCAGCTGAGGCCATTATATGAAGAGTATGTGGTCTTGAAAAATGAGATGGCAAGA  GCAAATCATTATGAGGACTATGGGGATTATTGGAGAGGAGACTATGAAGTAAATGGGGTAGATGGCTATG  ACTACAGCCGCGGCCAGTTGATTGAAGATGTGGAACATACCTTTGAAGAGATTAAACCATTATATGAACA  TCTTCATGCCTATGTGAGGGCAAAGTTGATGAATGCCTATCCTTCCTATATCAGTCCAATTGGATGCCTC  CCTGCTCATTTGCTTGGTGATATGTGGGGTAGATTTTGGACAAATCTGTACTCTTTGACAGTTCCCTTTG  GACAGAAACCAAACATAGATGTTACTGATGCAATGGTGGACCAGGCCTGGGATGCACAGAGAATATTCAA  GGAGGCCGAGAAGTTCTTTGTATCTGTTGGTCTTCCTAATATGACTCAAGGATTCTGGGAAAATTCCATG  CTAACGGACCCAGGAAATGTTCAGAAAGCAGTCTGCCATCCCACAGCTTGGGACCTGGGGAAAGGCGACT  TCAGGATCCTTATGTGCACAAAGGTGACAATGGACGACTTCCTGACAGCTCATCATGAGATGGGGCATAT  TCAGTATGATATGGCATATGCTGCACAACCTTTTCTGCTAAGAAATGGAGCTAATGAAGGATTCCATGAA  GCTGTTGGGGAAATCATGTCACTTTCTGCAGCCACACCTAAGCATTTAAAATCCATTGGTCTTCTGTCAC  CCGATTTTCAAGAAGACAATGAAACAGAAATAAACTTCCTGCTCAAACAAGCACTCACGATTGTTGGGAC  TCTGCCATTTACTTACATGTTAGAGAAGTGGAGGTGGATGGTCTTTAAAGGGGAAATTCCCAAAGACCAG  TGGATGAAAAAGTGGTGGGAGATGAAGCGAGAGATAGTTGGGGTGGTGGAACCTGTGCCCCATGATGAAA  CATACTGTGACCCCGCATCTCTGTTCCATGTTTCTAATGATTACTCATTCATTCGATATTACACAAGGAC  CCTTTACCAATTCCAGTTTCAAGAAGCACTTTGTCAAGCAGCTAAACATGAAGGCCCTCTGCACAAATGT  GACATCTCAAACTCTACAGAAGCTGGACAGAAACTGTTCAATATGCTGAGGCTTGGAAAATCAGAACCCT  GGACCCTAGCATTGGAAAATGTTGTAGGAGCAAAGAACATGAATGTAAGGCCACTGCTCAACTACTTTGA  GCCCTTATTTACCTGGCTGAAAGACCAGAACAAGAATTCTTTTGTGGGATGGAGTACCGACTGGAGTCCA  TATGCAGACCAAAGCATCAAAGTGAGGATAAGCCTAAAATCAGCTCTTGGAGATAGAGCATATGAATGGA  ACGACAATGAAATGTACCTGTTCCGATCATCTGTTGCATATGCTATGAGGCAGTACTTTTTAAAAGTAAA  AAATCAGATGATTCTTTTTGGGGAGGAGGATGTGCGAGTGGCTAATTTGAAACCAAGAATCTCCTTTAAT  TTCTTTGTCACTGCACCTAAAAATGTGTCTGATATCATTCCTAGAACTGAAGTTGAAAAGGCCATCAGGA  TGTCCCGGAGCCGTATCAATGATGCTTTCCGTCTGAATGACAACAGCCTAGAGTTTCTGGGGATACAGCC  AACACTTGGACCTCCTAACCAGCCCCCTGTTTCCATATGGCTGATTGTTTTTGGAGTTGTGATGGGAGTG  ATAGTGGTTGGCATTGTCATCCTGATCTTCACTGGGATCAGAGATCGGAAGAAGAAAAATAAAGCAAGAA  GTGGAGAAAATCCTTATGCCTCCATCGATATTAGCAAAGGAGAAAATAATCCAGGATTCCAAAACACTGA  TGATGTTCAGACCTCCTTTTAGAAAAATCTATGTTTTTCCTCTTGAGGTGATTTTGTTGTATGTAAATGT TAATTTCATGGTATAGAAAATATAAGATGATAAAAATATCATTAAATGTCAAAACTATGACTCTGTTCAG-3' Figure 4 . mRNA sequence of the human protein receptor ACE2. The green 5'-3' seed subsequence of length 10 is the reverse of an RNA sequence of the protein S of SARS-CoV-2. The probability to observe such an anti-match of length 10 by chance in a sequence of 2581 nucleotides equals 0.003.
The classical protein-protein interaction of the spicule protein S of SARS-CoV-2 is with the human protein receptor ACE2, but there exists a putative miRNA-like translation inhibition due to a subsequence (in green) of the protein S gene ( Figure 3 ) matching the ACE2 mRNA ( Figure 4 ). The human endogenous retrovirus HERV-K102 [32] has been described as having an antagonizing power on HIV-1 replication, by stimulating antibody production. It is indeed capable of high replication rate in vivo and in vitro and this high particle production can stimulate an early protective innate immune response against HIV-1 replication. It could play the same role in SARS-CoV-2. A possible mechanism of this immune stimulation could be due to the fact that both Gag protein of HERV-K107 and protein S of SARS-CoV-2 share common sub-sequences as the subsequence of length 15 nucleotides from the protein S of the SARS-CoV-2 given in green on Figure AAACACAAGGAAAAAATCCCAGAAAGAAACGGAAGGTTTACATTGCGAATATGTAGCAGAGCCGGTAATG  GCTCAGTCAACGCAAAATGTTGACTATAATCAATTACAGGAGGTGATATATCCTGAAACGTTAAAATTAG  AAGGAAAAGGTCCAGAATTAGTGGGGCCATCAGAGTCTAAACCACGAGGCACAAGTCATCTTCCAGCAGG  TCAGGTGCCCGTAACATTACAACCTCAAAAGCAGGTTAAAGAAAATAAGACCCAACCGCCAGTAGCCTAT  CAATACTGGCCTCCGGCTGAACTTCAGTATCGGCCACCCCCAGAAAGTCAGTATGGATATCCAGGAATGC  CCCCAGCACCACAGGGCAGGGCGCCATACCCTCAGCCGCCCACTAGGAGACTTAATCCTACGGCACCACC  TAGTAGACAGGGTAGTGAATTACATGAAATTATTGATAAATCAAGAAAGGAAGGAGATACTGAGGCATGG  CAATTCCCAGTAACGTTAGAACCGATGCCACCTGGAGAAGGAGCCCAAGAGGGAGAGCCTCCCACAGTTG  AGGCCAGATACAAGTCTTTTTCGATAAAAATGCTAAAAGATATGAAAGAGGGAGTAAAACAGTATGGACC  CAACTCCCCTTATATGAGGACATTATTAGATTCCATTGCTCATGGACATAGACTCATTCCTTATGATTGG  GAGATTCTGGCAAAATCGTCTCTCTCACCCTCTCAATTTTTACAATTTAAGACTTGGTGGATTGATGGGG  TACAAGAACAGGTCCGAAGAAATAGGGCTGCCAATCCTCCAGTTAACATAGATGCAGATCAACTATTAGG  AATAGGTCAAAATTGGAGTACTATTAGTCAACAAGCATTAATGCAAAATGAGGCCATTGAGCAAGTTAGA  GCTATCTGCCTTAGAGCCTGGGAAAAAATCCAAGACCCAGGAAGTACCTGCCCCTCATTTAATACAGTAA  GACAAGGTTCAAAAGAGCCCTATCCTGATTTTGTGGCAAGGCTCCAAGATGTTGCTCAAAAGTCAATTGC  CGATGAAAAAGCCCGTAAGGTCATAGTGGAGTTGATGGCATATGAAAACGCCAATCCTGATGTCAATCAG CCATTAAGCCATTAA-3' Figure 5 . Complete RNA sequence of the Gag protein of the virus HERV-K102 [36] . The green subsequence of length 14 (271-285) is present in the RNA sequence of the protein S of virus SARS-CoV-2 [22] . The probability to observe this match of length 14 by chance in a sequence of 1475 nucleotides equals 10 -6 .
When we combine the antibody power originated by the endogenous human retrovirus HERV-K102 envelop protein (whose part of its mRNA is shared by the SARS-CoV-2 protein S [36] ) with the putative inhibitory role of circRNAs capable to block the miRNA-like action of SARS-CoV-2, one could understand why certain carriers of SARS-CoV-2 are completely asymptomatic and therefore, by mimicking their defence mechanisms, consider a possible therapy against SARS-CoV-2. Indeed, if we look on the "sponge effect" of circRNAs against microRNAs [37] [38] [39] , one can consider a therapeutic effect erasing pathogenic actions of microRNAs.
For example, in the case of the human let-7e microRNA, a sub-sequence of human circular RNA PVT1 hybridizes hsa-let-7e ( Figure 6 ), thus preventing it from exerting a too important inhibition on the translation of proteins such as the gamma-globin 2. There exists a sub-sequence of the protein S of SARS-CoV-2 ( Figure 6 ), on which a similar action would be possible, hence reducing the miR-like pathogenicity of the protein S, but with less efficiency, with a hybridization free energy ΔG equal to -4.6 kcal/mol vs -11 for the hsa-let-7e. Figure 6 . RNA sub-sequence of the circPVT1 [22] . The RNA sequence in red is the microRNAs hsa miR let-7 inhibited by its "sponge" hsa-circ-PVT1. The RNA sequence in green is a sub-sequence of the protein S of SARS-CoV-2 on which hsa-circ-PVT1 could serve as inhibitor. Anti-match probability of a sub-sequence of length 9 in a sequence of length 1946 is 0.06 (resp. 0.03) for the red (resp. green) subsequence.
We can also compare the putative miRNA-like inhibitory efficacy of the protein S in other coronaviruses than SARS-CoV-2. By taking for example the SARS CoV Rs672 virus observed in 2006, it is possible to exhibit in the RNA sequence of its protein S gene some sub-sequences similar to those from SARS-CoV-2 involved in a miRNA inhibitory effect (Figure 7) : they have less nucleotides antimatching their protein targets, which could explain lesser virulence of the SARS epidemic than of the SARS-CoV-2 outbreak. Among the symptoms of the Covid-19 disease, anosmia is frequently described. This defect could be due to a miRNA-like inhibition of mRNAs of genes from olfactory receptor family (Figure 8 ). 
The perspectives of the present work are in the more in-depth study of unconventional mechanisms of action of the SARS-CoV-2 virus, in particular those concerning the disturbances of oxygen transport observed in many patients [41, 42] . We can also notice the resemblance of a SARS-CoV-2 sub-sequence with hsa-miR-let-7b, the microRNA the most upregulated in Kawasaki disease [43] described as potentially linked to SARS-CoV-2 infection [44] . The SARS-CoV-2 virus could have, more than a direct protein-protein interaction (proposed in [16] despite the criticisms of [45]), an effective inhibitory action in vivo of the same type as that predicted here in silico on the synthesis of subunits of human hemoglobin, and this action is more important for SARS-CoV-2 than for other coronaviruses (like the SARS CoV Rs672 on Figure 8 ). This hypothesis is in agreement with numerous studies showing a decrease of adult human hemoglobin blood concentrations in severe Covid-19 cases [46, 47] , presenting an increase of the high-sensitivity C-reactive protein as one of the three major predictors of severity [48] , like in ß-thalassemia [49] and viral infections [50] . Hence, one could envisage a therapy blocking pathologic inhibitor effects on ribosomal translation of hemoglobin subunits, using for example circular RNAs as blockers of possible viral miRNA-like mechanisms (Figure 7 ) [51] [52] [53] [54] . Another direction could be to search if furin cleavage site sub-sequence has the same type of interaction with key proteins like Rac small GTPase (a protein from the Rho GTPase family, which is a strong determinant of the virus-induced IFNbeta response [55] [56] ), implicated in replication of many important viral pathogens infecting humans or like interferons. A first example is given by the human small GTPase 1 (Figure 9 ) in which the inhibition of the SARS-CoV-2 protein S gene is possibly obtained through the same miRNA-like subsequence as for all type 1 interferons. The host immune system is indeed reacting to viral intrusion first with synthesis of type I interferons IFNalphas and IFNbetas [57] [58] . They are messengers allowing the activation of cellular defenses blocking viral replication. In humans, these type I interferons are bound to interferon receptors, and then, they induce proteins with antiviral actions: RNA-dependent protein kinase (PKR), 2′,5′oligoadenylate synthetase (OAS), RNase L, and Mx protein GTPases [59] . In the first case, the sequence is the whole mRNA of IFNA7 and the probability to observe such an anti-match of length 8 by chance in a sequence of 730 nucleotides equals 0.04. In the second case, the sequence of the whole mRNA of IRF1 contains to targets and the probability to observe the last antimatch of length 11 by chance in a sequence of 1032 nucleotides equals 2 10 -3 . In red, miRNA inhibiting sequences [59] [60] . The probability to observe by chance the micro-RNA hsa miR let-7b-5p anti-match of length 9 in the first 730-length sequence equals 0.02 and the micro-RNA hsa miR 301a-3p anti-match of length 9 in the second 1032-length sequence equals 0.016.
In the same way, the miRNA-like subsequence of SARS-CoV-2 protein S gene from its furin cleavage site) anti-matches the mRNA of the MCT1 gene involved in the lactate shuttle between astrocytes and neurons ( Figure 11 ) and this effect decreases the energy provided to the brain [61] . That could explain some neurological and neuropsychiatric complications observed in SARS-COV-2 patients, since the earliest cohorts featured non-specific neurological symptoms, such as dizziness and headache. We can notice also that the protein S gene is not the only SARS-CoV-2 gene anti-matching important human molecules. It is for example the case of the ORF10 protein with the human gamma-globin 2 ( Figure 12 ). On Figure 12 , the free energy and enthalpy are given in kcal/mol for two hybridizations [65] [66] between subsequences of SARS-CoV-2 genes and subsequences of genes of two important proteins of the human metabolism of oxygen, involved in the oxygen transportation in adult for the first (the human hemoglobin beta-globin (HBG) subunit) and the in embryo for the second (the human hemoglobin gamma-globin 2 (HGG 2) subunit).
We have summarized the probabilities of anti-matches of Figures 2 to 11 and in Table 1 , allowing for the comparison between the classical miRNA action and the putative inhibitory influence the protein S gene of SARS-CoV-2 can have on the translation of important human proteins. 
To conclude, the natural history of the SARS-CoV-2 virus remains widely unknown and it is still too early to say whether the many mutations observed will cause it to evolve in a favorable direction from a human point of view. There are for example some mutations surely deleterious [66, 67] , but also others favoring the positive role of some human miRNAs against SARS-CoV-2 [68] [69] [70] suggesting a possible therapy. The present proposal of a miRNA-like mechanism would at least allow to see, for a predictive purpose, what mutations are keeping, losing or reinforcing its pathogenicity. 