Conservation of kinetoplastid minicircle characteristics without nucleotide sequence conservation

The nucleotide sequence and restriction fragment electrophoretic mobility of four minicircles from the kinetoplast DNA of Trypanosoma brucei were determined. Each minicircle possesses an approximately 130 base pair conserved sequence which occurs in other African trypanosome minicircles and contains a 13 base pair sequence that is conserved among kinetoplastid genera [Kidane et al. (1984) Gene 27, 265-277]. A sequence located adjacent to the conserved sequence conserves purine versus pyrimidine strand bias, but not nucleotide sequence, and contains periodic oligo(dA) tracts. Minicircle fragments containing the conserved sequence and adjacent segment exhibited anomalous electrophoretic mobility in polyacrylamide gels. The position of the oligo(dA) tracts in the fragments appears to influence this anomalous mobility. The presence of conserved features independent of conserved nucleotide sequence and the lack of conserved open reading frames among these minicircles suggests that minicircles may have a function other than encoding protein.