Characterization of kinetoplast minicircle DNA in the lower trypanosomatid Crithidia oncopelti

The kinetoplast DNA of the lower trypanosomatid Crithidia oncopelti contains minicircles of four major size classes. Attempts to clone these molecules revealed the unclonability of the full-length minicircles in pUC and M13 vectors. A few clones were obtained using a lambda insertion vector lambda XIII. The nucleotide sequence of a cloned, apparently full-length minicircle has been determined and characterized. This 1848-bp molecule contains a single region corresponding to the 'conserved' minicircle region in other trypanosomatid species and an area with some features of the bent helix. About one-third of the molecule length is occupied by an extremely (T+G) versus (A+C) strand biased region. The role of this region, as well as the significance of the ORFs found and the putative secondary structures potentially formed by the minicircle sequence, remains unknown. The hybridization of kDNA with the different regions of a cloned minicircle shows that there are some segments of DNA specific to a particular class or a group of classes. Such a mode of sequence heterogeneity suggests that the possible functions (if any) of different minicircle classes may differ.