Delineating the centromeric repeats on T. brucei chromosome 3 using long range restriction mapping. Chromosomal DNA was immobilised in agar blocks, restriction digested and fractionated by CHEFE (Methods). Blots were hybridised using the probes Tb7 and Tb20 (Additional file 1) (identified as yellow arrows, which also signify the direction of transcription). Fragment sizes derived in this study are shown on the schematic, with their predicted sizes (GeneDB) in parentheses. The location and inferred size of the ~147 bp repeat array (7.8 kb, GeneDB; 75/80 kb, this work) is shown (striped/filled box). The %GC content across the region is presented using Artemis , with the location of the repeat arrays shown in a blue box.