UV photomicrograph of remnants of mouse L1210 cells stained with acridine orange (400x magnification)
This remarkable photograph was taken at an Ohio State University laboratory over 20 years ago. To date, I have found nothing in the literature that matches it, much less any sort of explanation for what these circles might be. If anyone has come across something like this in the literature or in their laboratory, please e mail me at email@example.com.
Anyone who has ever taken a general biology course that describes DNA knows that viral and bacterial DNA is predominantly circular in nature. What is lesser known is that circular DNA can also be found within the eukaryotic genome, usually associated with DNA rearrangements during differentiation. Are these eukaryotic circular elements merely obscure curiosities; exceptions to the rule, or could they be something more? The prevailing dogma suggests that the genes within eukaryotic DNA are linearly arrayed, based on data originally acquired from chromosomal recombination and later “validated” by chromosomal sequencing data which involves “jumping over” and editing out sections of the DNA not amenable to sequencing protocols, i.e., DNA that is not linear in nature. When these troublesome sequences are removed from the equation, the bioinformatician can now splice together the remaining DNA into a product more to their liking: simple linear DNA. Yet problems remain. How can enhancer elements increase transcription when they may be thousands of base pairs away from the promoter? Currently, the prevailing answer in the literature is to bring them together into a loop so they can interact. Could it be that the loop was there to begin with before the DNA was manhandled into linear conformity? If eukaryotic circular DNA is the exception, rather than the rule to eukaryotic chromosomal structure, how does one go about explaining the photomicrograph shown above? DNA stains bright green when exposed to acridine orange.
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