Within months of the first reports of pneumonia caused by a previously unknown virus emerging from Wuhan, town centres across the UK became eerily deserted, millions faced delayed and cancelled NHS treatment and the national debt reached levels not seen since the Second World War. Researchers developed vaccines in a remarkably short time. Yet, as soon as SARS-CoV-2 emerged, virologists feared the pathogen would mutate into something worse. Now variants of concern (VOC) from Britain, South Africa and Brazil raise the prospect that SARS CoV-2 would escape the protection offered by vaccines and possibly evolve into a more infectious and deadly strain. This article looks at the biology behind the headlines.
Coronaviruses have the largest RNA genome of, so far as we know, any virus.1 SARS-CoV-2 carries its genetic code as a single strand of RNA containing about 30,000 nucleotides (adenine, cytosine, guanine or uracil).1,2 This encodes 29 proteins, including the now infamous spike: a chain of about 1260 amino acids. As we will see, the length of the spike depends on the variant.1,3-5 The length of the spike on the outside of the virus contains about 672 amino acids. The remainder of the chain spans the viral membrane.4 The other proteins, for example, allow the virus to build copies, help SARS-CoV-2 avoid our immune defences, and encase and protect the viral RNA.3