Then they infected these cells with the SARS-CoV-2 virus, and reported that the SARS-CoV-2 viral RNA is converted into DNA. To prove their claims in an experimental setup, the authors genetically altered cells to make proteins that can perform reverse transcription. So the chimeric viral and human RNA could just be an artefact of the RNA-seq process, since reverse transcriptases are known to mix and match target sequences. The authors appear to have overlooked the fact that in the process of preparing a sample for RNA-seq, the scientist must herself artificially reverse transcribe RNA into DNA – because only DNA can be sequenced (for further study). This data may seem convincing at first glance, but the devil is in the details. The authors reported that in cells infected with SARS-CoV-2, there were some viral RNA sequences interspersed between RNA sequences of human genes. So a RNA-seq’s output is a sort of measure of all the genes that are active in the target cell. The observation banks on a powerful tool called RNA-seq, which provides the sequences of all the RNA molecules produced by a cell. The authors’ claims are based largely on one primary observation and one experiment. This process differs from what retroviruses like HIV do routinely: they use their own proteins to convert and mix the DNA. The paper claims these LINEs do the same thing with parts of the novel coronavirus’s RNA as well. The human genome has multiple LINEs – effectively, parts of our DNA responsible for reverse-transcribing human RNA into DNA, and integrating it into the human DNA at a different part. Their explanation is based on a group of genetic entities called long interspersed nuclear elements (LINE). The paper claimed, outlandishly, that parts of the SARS-CoV-2 viral RNA could be reverse transcribed into DNA and integrated into the human genome.Īccording to the paper’s authors, they were attempting to explain why some COVID-19 patients showed signs of the virus in RT-PCR tests even weeks after recovering from the disease.
This is why a preprint paper uploaded to the bioRxiv preprint server on December 13 caught the scientific community by surprise. It’s also unusual – maybe even impossible – to have members of one class of viruses show fundamental properties associated with another.Īlso read: Why Is It so Difficult to Fight HIV? In all, there are seven families, or groups, of viruses, and each group specifies special adaptations, refined over years of evolution, often through several hosts. Viruses like HIV and Rous sarcoma belong to this family. Such viruses – called retroviruses – violate the central dogma because information first flows from RNA to DNA, and then from the DNA to the RNA to proteins. A virus then mixes this DNA with the DNA of its host, thus becoming part of the host forever. They found viruses that could make a DNA copy with their RNA using an enzyme called reverse transcriptase, in a process called reverse transcription. These viruses also deviate from the central dogma only slightly: there is no DNA, but the information flows only from the RNA to proteins.īut what Temin and Baltimore discovered in 1970 was a proper exception to the central dogma. The influenza, hepatitis C and SARS-CoV-2 viruses are in this category. Some viruses contain the machinery to make copies of their RNA, and they don’t have a DNA component in their life cycle whatsoever. To propagate itself, each virus makes a copy of the information in its genetic material to pass onto its ‘daughter’ viruses. There are different kinds of RNA-containing viruses. Viruses are the only known life-forms that can use RNA as their genetic material. This is because they can be both alive and not alive – a feature that demands that taxonomists also consider other attributes that make viruses different.Īnother such feature is their genetic material. However, viruses are not classified the same way as other life forms. Viruses, like other living beings, come in all shapes and sizes, and are classified into different families. In this year, Howard Temin and David Baltimore found something odd in one group of viruses. And everywhere scientists looked, they realised all organisms followed this dogma – until 1970. He suggested that information always flows in living beings from DNA – a stable, inheritable molecule – through a relatively unstable intermediate, the messenger RNA, and then onto proteins, which are the workhorses of all life functions. In September 1957, Francis Crick proposed the ‘central dogma of molecular biology’.
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