Quantitation of genetic differences between Trypanosoma brucei gambiense, rhodesiense and brucei by restriction enzyme analysis of kinetoplast DNA.

We have compared a total of 44 recognition sites for 12 restriction endonucleases on the 20 kilobase pair maxi-circle of kinetoplast DNA from nine Trypanosoma brucei stocks, four which are known to be infective to man (tow 'gambiense' and two 'rhodesiense' variants). In addition to five polymorphic sites, these DNAs differ in the size of a 5 kilo-base pair region which is cleaved only by one of the restriction enzymes tested and which varies in size over 1.5 kilo-base pairs. Our analysis shows that the maxi-circle sequences of these stocks are very similar, the maximal calculated difference between any two being 3%. A relatively large difference was found between a rhodesiense stock from uganda and one from Zambia, confirming the distinction between northern and southern East African rhodesiense stocks found by analysis of enzyme polymorphisms (Gibson et al. (1980) Adv. Parasitol. 18, 175-246). The gambiense variants could not be identified by unique restriction site polymorphisms, but contained the smallest maxi-circle found thus far in T. Brucei. Our results indicate that T. brucei stocks infective and not infective to man are so closely related as to preclude their differentiation by analysis of kinetoplast DNA. This analysis is useful, however, in providing quantitative information about relatedness of stocks.