A Long Standing Rule Faces a New Test
The central dogma of molecular biology describes how genetic information generally moves between DNA, RNA and proteins. While scientists have discovered several exceptions over the years, the basic principle that information does not flow from proteins back into nucleic acids has remained intact.
Now, two new studies have identified an unusual bacterial system that pushes the boundaries of this rule.
The Strange Role of Reverse Transcriptases
The discovery involves a family of bacterial enzymes called defence-associated reverse transcriptases, or DRTs. These enzymes help bacteria defend themselves against bacteriophages—viruses that infect bacteria.
A newly described system, called DRT3, uses two enzymes that work together to produce DNA during a phage attack.
DNA Made Without a Normal Template
One of the most unusual features of DRT3 is how its second enzyme, DRT3b, produces DNA.
Normally, DNA synthesis depends on another nucleic-acid strand acting as a template. DRT3b, however, can produce a DNA strand without using a nucleic-acid template. Instead, the protein itself determines the order in which certain DNA building blocks are added.
A Simple but Remarkable DNA Sequence
Researchers found that DRT3b produces an ordered sequence involving alternating cytosine and adenine bases, rather than generating a random string of DNA.
The sequence itself is simple, but the mechanism is highly unusual because a protein is effectively determining the sequence of a nucleic acid. That makes the discovery particularly interesting for molecular biology.
How Does It Help Bacteria?
The DRT3 system appears to be part of a bacterial defence strategy. During a phage infection, the system can become activated and cause unusual DNA to accumulate inside the bacterial cell.
This buildup can push the infected cell into a dormant or shutdown state, preventing the invading virus from successfully reproducing and spreading.
Does This Really Break the Central Dogma?
Not quite.
The finding is remarkable because it shows information flowing from a protein into a defined DNA sequence. However, scientists stress that this does not overturn Francis Crick’s central dogma.
The central principle concerns the inability of information stored in a protein sequence to be transferred back into nucleic acids in a way that reconstructs the original genetic information. DRT3b produces a limited, highly repetitive DNA sequence rather than recovering genetic information from a protein.
Why the Discovery Matters
The research highlights how much more complicated biological information systems can be than textbook diagrams suggest. It could also provide new insights into bacterial defence mechanisms and the evolution of molecular systems.
Rather than destroying a foundational rule of biology, DRT3 appears to show just how creatively nature can operate around its boundaries.