New discovery shows human cells can write RNA sequences into DNA

PHILADELPHIA – Cells contain machines that duplicate DNA into a new set that goes into a newly formed cell. This same class of machines, called polymerases, also creates RNA messages, which are like notes copied from the central repository of DNA recipes, so that they can be read more efficiently into proteins. But it was believed that polymerases only worked in one direction from DNA to DNA or RNA. This prevents RNA messages from being rewritten into the main genomic DNA cookbook. Now, researchers at Thomas Jefferson University are providing the first evidence that RNA segments can be rewritten into DNA, potentially challenging the central dogma of biology and could have broad implications affecting many fields. of biology.

“This work opens the door to many other studies that will help us understand the importance of having a mechanism to convert RNA messages to DNA in our own cells,” says Richard Pomerantz, PhD, associate professor of biochemistry and of Molecular Biology at Thomas Jefferson University. . “The reality that a human polymerase can do this with great efficiency raises many questions. For example, this finding suggests that RNA messages can be used as templates to repair or rewrite genomic DNA.

The work was published on June 11 in the journal Scientists progress.

With first author Gurushankar Chandramouly and other collaborators, Dr Pomerantz’s team began by studying a very unusual polymerase, called theta polymerase. Of the 14 DNA polymerases found in mammalian cells, only three do most of the work of duplicating the entire genome to prepare for cell division. The other 11 are mainly involved in the detection and repair of breaks or errors in DNA strands. Theta polymerase repairs DNA, but is very error prone and causes many errors or mutations. The researchers therefore noticed that some of the “bad” qualities of theta polymerase were those that it shared with another cellular machine, although one more common in viruses – reverse transcriptase. Like Pol theta, HIV reverse transcriptase acts like DNA polymerase, but can also bind to RNA and read RNA back into a strand of DNA.

In a sleek series of experiments, the researchers tested theta polymerase against HIV reverse transcriptase, which is one of the best-studied of its kind. They showed that theta polymerase was able to convert RNA messages to DNA, which it did as well as HIV reverse transcriptase, and actually did a better job than when duplicating DNA into DNA. Theta polymerase was more efficient and introduced fewer errors when using an RNA template to write new DNA messages than when duplicating DNA into DNA, suggesting that this function could be his main focus in the cell.

The group collaborated with the lab of Dr. Xiaojiang S. Chen at USC and used X-ray crystallography to define the structure and found that this molecule was able to change shape in order to adapt to the d molecule. Bigger RNA – a feat unique among polymerases.

“Our research suggests that the main function of theta polymerase is to act as a reverse transcriptase,” explains Dr. Pomerantz. “In healthy cells, the purpose of this molecule may be the repair of DNA by RNA. In unhealthy cells, such as cancer cells, theta polymerase is highly expressed and promotes cancer cell growth and Drug resistance. It will be exciting to better understand how RNA theta polymerase activity contributes to DNA repair and cancer cell proliferation. “

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This research was funded by NIH grants 1R01GM130889-01 and 1R01GM137124-01, and R01CA197506 and R01CA240392. This research was also funded in part by a grant from the Tower Cancer Research Foundation. The authors do not report any conflict of interest.

Article reference : Gurushankar Chandramouly, Jiemin Zhao, Shane McDevitt, Timur Rusanov, Trung Hoang, Nikita Borisonnik, Taylor Treddinick, Felicia Wednesday Lopezcolorado, Tatiana Kent, Labiba A. Siddique, Joseph Mallon, Jacklyn Huhn, Zainab Shoda, Ekaterina Kashjiang Starkand Xiaoji Chen and Richard T. Pomerantz, “Pol theta reverse transcribes RNA and promotes RNA-based DNA repair”, Science Advances, DOI: 10.1126 / sciadv.abf1771, 2021.

Media contact: Edyta Zielinska, 267-234-3553, [email protected]

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