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sadie's avatar

Who really knows just how intrusive and dangerous this thing is.... the deeper you go the more questions it raises. What does the spike area look like in sars1 as compared to sars2? Do you know what type of vaccines were tried on sars1?

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Brian Mowrey's avatar

Ancestral sequence is text-converted in the upload at my resource hub... though the linebreak-free segment is at the bottom of the document and harder to find / understand https://unglossed.substack.com/p/unglossed-resource-hub

Initiation is more a question of physical RNA structure and whether this promotes ribosomal entry and synthesis at a particular "atg" (aug). For the virus, this in turn is a question of a given atg's proximity and relationship with the nearest upstream body regulatory sequence, which is like a notch in the sequence between every coding protein that allows fixing on a copy of Orf1's template leader sequence, which is the ribosomal entry promoter. So generally only atg's that are 5'-proximate in a given coding protein are eligible for consideration as alternate initiation sites. These can result in functional internal ORFs if the leader sequence gets fixed to the atg in question, or if cellular ribosomes tend to slip past the canonical atg and land on the atg in question more than rarely. A third way to get unexpected proteins is fusion via deletion, so say a subgenomic spike RNA molecule is being printed out but it suddenly skips some monomers, maybe that's going to make an unexpected hybrid protein of some type.

For N protein, for example, with my w's for c's substitution, the ancestral sequence looks like:

taaawgaawaaawtaaaatgtwtgataatggawww

where taa is the STOP for Orf8, awgaaw is the TRS-B that promotes attaching a copy of the TRS-L, first atg starts N protein, second atg starts Orf9b protein - the second atg is only +10 monomers of the first.

For spike it's different, the first downstream atg is not until +180 monomers, but it's +204 atg that is suspected as an iORF, see S iORF1 on Fig 4 https://www.nature.com/articles/s41586-020-2739-1. This coincidentally is over one of the commonly used primers and featured in the Single Gene Target Failure that marks Alpha, BA.1, and some of the BA.2/4/5 mutants in PCR. So maybe the virus keeps trying to kick out this iORF because it parasitizes spike expression.

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