THE TELOMERIC GGGTTA REPEATS OF TRYPANOSOMA-BRUCEI CONTAIN THE HYPERMODIFIED BASE-J IN BOTH STRANDS

We have previously shown that nuclear DNA of bloodstream form Trypanos oma brucei contains a novel base beta-glucosyl-hydroxymethyluracil, ca lled J. Base J is enriched in minichromosome fractions but not in the minichromosome internal repeats, suggesting the association of J with telomeric DNA, To test whether J is present in the long telomeric (GGG TTA)(n) repeat arrays, which are 2-26 kb in T.brucei, we have purified these arrays both by hybrid selection and by isolating 2-26 kb fragme nts from DNA digested with multiple restriction enzymes, We find that in purified telomeric repeats similar to 13% of T is replaced by J, co mpared to 0.8% in total DNA, and we estimate that similar to 50% of th e total J is In these repeats, Highly purified complementary strands o f the repeats were obtained by alkaline CsCl equilibrium centrifugatio n, In the (TAACCC)(n) strand 14% of T was replaced by J, In the (GGGTT A)(n) strand similar to 36% of the second T was replaced by J; the fir st T was not detectably replaced, Modified bases have not been found i n telomeric repeats before, How the bulky base J affects telomere func tion and structure in bloodstream form trypanosomes remains to be dete rmined.