Selective amplification of maxicircle classes during the life cycle of Leishmania major.

The kinetoplast genome contains several thousands of minicircles of various sequence classes and several scores of maxicircles. We demonstrated that maxicircles are heterogeneous in clonal cultures of Leishmania major, and, therefore, probably heterogeneous (heteroplasmic) within the kinetoplast. Sequence heterogeneity was observed in a non-coding fragment upstream of the 12S rRNA gene. We identified about 20 stable variants of this fragment, which were composed of one to five non-identical repeats 200-300bp in length. Promastigote-to-amastigote and amastigote-to-promastigote differentiation was often accompanied by shifts in abundance of some maxicircle classes. Reversion to promastigote-specific maxicircle patterns was usually observed in the life cycle (promastigote-amastigote-promastigote), however there were many exceptions.