Scientists have found a mechanism that theoretically allows the coronavirus to channel its genetic material into our DNA.
Virologist Friedemann Weber explains what is behind the study – and what the results mean for the vaccination.
A few weeks ago, a study from the United States caused a stir. Researchers wanted to have found proof that the coronavirus can smuggle small fragments into our DNA.
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A new study now provides clues as to the mechanism that could be behind this.
RNA becomes DNA
The human genome consists of so-called DNA (deoxyribonucleic acid). In the case of RNA viruses, which also include Sars-CoV-2, the genetic information consists of RNA (ribonucleic acid). RNA has a slightly different structure than DNA. In order for viral RNA to get into the human genome, it has to be transcribed into DNA by biological tools and then incorporated into the genome.
The theory that exactly this can happen was put forward by US researchers, among others. The reason for the investigation were PCR tests, some of which were positive weeks or even months after the infection. The scientists then put forward the thesis that the RNA of the coronavirus is included in the human genome.
Researchers found viral RNA in human cells
To investigate the question of PCR positivity, the scientists examined the cells of patients who had previously contracted Covid-19. These included patients who tested positive for the virus again using a PCR test 60 or more days after a positive corona test. In around 90 percent of the cases, there was no Sars-CoV-2 infection despite a positive PCR test, so there was no renewed infection.
According to their own information, the researchers then found, in very rare cases, genetic fragments of the coronavirus in the genome of people who had been infected with the pathogen some time before. They also tried to replicate the integration in laboratory tests. Accordingly, they succeeded in introducing short fragments of the virus genome into the genome of cultured human cell lines.
The study, published in the journal of the US National Academy of Sciences “PNAS”, is by no means unchallenged.
“There are now two manuscripts from other scientists who strongly question this study,” explains virologist Dr. Weber. The US researchers are accused of having investigated a methodological error. The virus detection in the genome is therefore wrong.
“So at the moment we don’t even know whether the virus can even integrate into the genome, i.e. the DNA,” Weber emphasizes. So it has not yet been ensured that Sars-CoV-2 can be smuggled into the DNA.
New study reveals mechanism for RNA integration
And although this is not yet clear, another study may have already found an explanation for a theoretically possible mechanism. With the study recently published in the journal “Science Advances”, a team led by Gurushankar Chandramouly from Thomas Jefferson University in Philadelphia demonstrated for the first time that an enzyme (polymerase) in humans can translate RNA segments back into DNA.
Sars-CoV-2 could theoretically make use of this mechanism and thus smuggle small fragments of its RNA into the DNA of an infected person. For virologist Weber “exciting, but not particularly worrying”, and for several reasons.
Rewriting the RNA is a repair mechanism
“On the one hand, most of our chromosomes are non-coding,” explains the virologist. So only small parts of it are so active that a change could come from them.
On the other hand, what the study shows using the polymerase is actually a repair mechanism.
You can imagine it like at the dentist. If he finds a hole, he first drills it a little further and then fills it. It works the same way with DNA.
The polymerase is responsible for this repair. It comes across such holes and then tries to fill them.
“So far we knew that the polymerase takes the DNA as a template and can then rewrite it to DNA or RNA in order to fill holes,” explains Weber.
The new study now shows that it is also possible the other way around. It can also transcribe RNA to DNA.
Polymerase only builds very small pieces of virus
So, in principle, would it be possible for small scraps of the Corona genome to be built into ours? Theoretically yes.
But: “If that were the case, it would happen to every virus,” explains virologist Weber.
We are constantly confronted with viruses, with RNA viruses, and also with DNA viruses. If that were a common mechanism and posed a problem, we would already know. A possible incorporation of parts of the virus into the DNA of individual cells must be even rarer compared to the already very low natural mutation rate of our chromosomes.
In addition, the polymerase could only recreate very small pieces of the virus, if at all.
“The study showed a little more than 50 nucleotides, i.e. building blocks. However, the coronavirus has more than 30,000 of these nucleotides. This means that only very small parts of it can be installed anyway,” Weber explains.
The probability that this will happen, however, is “very, very small”.
“Not just because it is such a rare occurrence in general. But also because the polymerase in question is not even present in most tissues.”
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Covid-19 has more impact on cells than vaccination
The question that may now arise: If the coronavirus could theoretically change our DNA, couldn’t a vaccine also?
“In biology, you can rarely exclude anything 100 percent. But it is certainly not the rule that something is constantly being built into our DNA,” says virologist Weber.
“The vaccine is initially just mRNA. Now this can theoretically be rewritten. However, it would then have to be installed in a second step. It is very unlikely that this will happen.”
The virus is “armed to the teeth” and demands a lot more from the body than a vaccination does. It also has more influence on many cellular factors that set the defense in motion, for example. A vaccination, on the other hand, works much more specifically and therefore also evokes a more targeted defense reaction.
The researchers in the polymerase study also do not assume that information from the mRNA vaccines could get into the genome. This would require a so-called “primer”, a start sequence that first sets the translation in motion. However, this sequence is missing in the vaccines.
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“The probability that virus genetic material will be incorporated into our DNA through an infection or vaccination is negligible,” says virologist Weber.
“It would only be a problem if it were done systematically. And there is no evidence of that. So we don’t have to worry.”
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