beta-D-glucosyl-hydroxymethyluracil is a conserved DNA modification in kinetoplastid protozoans and is abundant in their telomeres.
The unusual DNA base beta-D-glucosyl-hydroxymethyluracil, called "J, " replaces approximately 0.5-1% of Thy in DNA of African trypanosomes but has not been found in other organisms thus far. In Trypanosoma brucei, J is located predominantly in repetitive DNA, and its presence correlates with the silencing of telomeric genes. Using antibodies specific for J, we have developed sensitive assays to screen for J in a range of organisms and have found that J is not limited to trypanosomes that undergo antigenic variation but is conserved among Kinetoplastida. In all kinetoplastids tested, including the human pathogens Leishmania donovani and Trypanosoma cruzi, J was found to be abundantly present in the (GGGTTA)n telomere repeats. Outside Kinetoplastida, J was found only in Diplonema, a small phagotrophic marine flagellate, in which we also identified 5-MeCyt. Fractionation of Diplonema DNA showed that the two modifications are present in a common genome compartment, which suggests that they may have a similar function. Dinoflagellates appear to contain small amounts of modified bases that may be analogs of J. The evolutionary conservation of J in kinetoplastid protozoans suggests that it has a general function, repression of transcription or recombination, or a combination of both. T. brucei may have recruited J for the control of genes involved in antigenic variation.[1]References
- beta-D-glucosyl-hydroxymethyluracil is a conserved DNA modification in kinetoplastid protozoans and is abundant in their telomeres. van Leeuwen, F., Taylor, M.C., Mondragon, A., Moreau, H., Gibson, W., Kieft, R., Borst, P. Proc. Natl. Acad. Sci. U.S.A. (1998) [Pubmed]
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