Cells contain machinery that duplicates DNA into a new latest set that goes into a newly formed cell. that very same class of machines, called polymerases, also build RNA messages, which are like notes copied from the central DNA repository of recipes, in order that they are often read more efficiently into proteins. But polymerases were thought to only work in 1 direction DNA into DNA or RNA. This prevents RNA messages from being rewritten back to the master recipe book of genomic DNA. Now, Jefferson University researchers provide the 1st evidence that RNA segments are often written back in-to DNA, which potentially challenges the central dogma in biology and might have wide implications affecting many fields of biology.
“This work opens the door to several other studies which will help us understand the importance of having a mechanism for converting RNA messages into DNA in our own cells,” says Richard Pomerantz, PhD, professor of biochemistry and biology at Jefferson University. “The reality that a person’s polymerase can do that with high efficiency, raises many questions.” for instance , this finding suggests that RNA messages are often used as templates for repairing or re-writing genomic DNA.
The work was published June 11th within the journal Science Advances.
Together with first author Gurushankar Chandramouly and other collaborators, Dr. Pomerantz’s team started by investigating one very unusual polymerase, called polymerase theta. Of the 14 DNA polymerases in mammalian cells, only three do the majority of the work of duplicating the whole genome to pre-pare for cell division . The remaining 11 are mostly involved in detecting and making repairs when there is a break or error within the DNA strands. Polymerase theta repairs DNA, but is extremely error-prone and makes many errors or mutations. The researchers therefore noticed that a number of polymerase theta’s “bad” qualities were ones it shared with another cellular machine, albeit another common in viruses — the reverse-transcriptase . Like Pol theta, HIV reverse-transcriptase acts as a DNA polymerase, but also can bind RNA and skim RNA back to a DNA strand.
In a series of elegant experiments, the researchers tested polymerase theta against the reverse-transcriptase from HIV, which is one among the best simplest studied of its kind. They showed that polymerase theta was capable of converting RNA messages into DNA, which it did also as HIV reverse-transcriptase, which it actually did a far better job than when duplicating DNA to DNA. Polymerase theta was more efficient and introduced fewer errors when using an RNA template to write down new DNA messages, than when duplicating DNA into DNA, suggesting that this function might be its primary purpose within the cell.
The group collaborated with Dr. Xiaojiang S. Chen’s lab at USC and used x-ray crystallography to define the structure and located that this molecule was ready to change-shape so as to accommodate the more bulky RNA molecule — a feat unique among polymerases.
“Our research suggests that polymerase theta’s main function is to act as a reverse-transcriptase,” says Dr. Pomerantz. “In healthy cells, the aim of this molecule could also be toward RNA-mediated DNA repair. In unhealthy cells, like cancer cells, polymerase theta is highly expressed & promotes cancer cell growth and drug resistance. it’ll be exciting to further understand how polymerase theta’s activity on RNA contributes to DNA repair and cancer-cell proliferation.”
This research was supported by NIH grants 1R01GM130889-01 & 1R01GM137124-01, & R01CA197506 and R01CA240392. This research was also supported partially by a Tower Cancer Research Foundation grant.
The research published on Science Advances.