Drug development is very hard because we don’t know all the players inside the cell. A recent paper describes an entirely new class of player — circular DNA derived from an ancient virus. The authoress is Laura Manuelidis, who would have been a med school classmate had I chosen to go to Yale med instead of Penn. She is the last scientist standing who doesn’t believe Prusiner’s prion hypothesis. She didn’t marry the boss’s daughter being female, so she married the boss instead; Elias Manuelidis a Yale neuropathologist who would be 99 today had he not passed away at 72 in 1992.
The circular DNAs go by the name of SPHINX an acronym for Slow Progressive Hidden INfections of X origin. They have no sequences in common with bacterial or eukaryotic DNA, but there some homology to a virus infecting Acinebacter, a wound pathogen common in soil and water.
How did she find them? By doggedly pursuing the idea the neurodegenerative diseases such as Cruetzfeldt Jakob Disease (CJD) and scrapie were due to an infectious agent triggering aggregation of the prion protein.
As she says: “The cytoplasm of CJD and scrapie-infected cells, but not control cells, also contains virus-like particle arrays and because we were able to isolate these nuclease-protected particles with quantitative recovery of infectivity, but with little or no detectable PrP (Prion Protein), we began to analyze protected nucleic acids. Using Φ29 rolling circle amplification, several circular DNA sequences of <5 kb (kilobases) with ORFs (Open Reading Frames) were thereby discovered in brain and cultured neuronal cell lines. These circular DNA sequences were named SPHINX elements for their initial association with slow progressive hidden infections of X origin."
SPHINX itself codes for a 324 amino acid protein, which is found in human brain, concentrated in synaptic boutons. Strangely, even though the DNAs are presumably viral derived, they contain intervening sequences which don't code for protein.
The use of rolling circle amplification is quite clever, as it will copy only circular DNA.
Stanley Prusiner is sure to weigh in. Remarkably, Prusiner was at Penn Med when I was and was even in my med school fraternity (Nu Sigma Nu) primarily a place to eat lunch and dinner. I probably ate with him, but have no recollection of him whatsoever.
Circular DNAs outside chromosomes are called plasmids. Bacteria are full of them. The best known eukaryote containing plasmids is yeast. Perhaps we have them as well. Manuelidis may be the first person to look.
Chemiotics II 