TRYPANOSOMA-BRUCEI - INHERITANCE OF KINETOPLAST DNA MAXICIRCLES IN A GENETIC CROSS AND THEIR SEGREGATION DURING VEGETATIVE GROWTH

The inheritance of maxicircle DNA was determined using a polymorphic E coRI restriction site in the maxicircle variable region. In 11 hybrid progeny from a genetic cross of two stocks of Trypanosoma brucei, 7 pr ogeny apparently inherited maxicircles uniparentally from either paren t, in agreement with the results from previous studies, but in 4 proge ny inheritance was biparental. Three subclones from 2 of these 4 proge ny were made,and in these the maxicircles of only one parental type we re detected. These data are considered in terms of a simple model wher eby half the maxicircle genomes are inherited from each parent into pr ogeny at meiosis with subsequent stochastic segregation at each mitoti c division. This model generates a quantitative prediction as to the p eriod of time required for fixation of inheritance to a uniparental pa ttern which provides a reasonable fit to the experimental data. These results provide an explanation as to why previous studies have shown t hat maxicircles are (apparently) inherited uniparentally: the kinetopl ast is a unitary organelle inherited faithfully at cell division, but the maxicircles that it contains are best considered as a population t hat divides stochastically. Consideration of the model also explains w hy maxicircle populations are homogeneous. (C) 1995 Academic Press, In c.