Evidence for kinetoplast and nuclear DNA homogeneity in Trypanosoma evansi isolates

Abstract

The kinetoplast DNA minicircles from 13 stocks of trypanosomes designated as Trypanosoma evansi were digested with various restriction enzymes. We also examined the distribution of restriction site polymorphisms in the nuclear DNA of 9 of these stocks, using 7 different variable surface glycoprotein (VSG) and non-VSG probes. Restricted kinetoplast DNA (kDNA) fragments of some of these strains were cloned into M13 or PUC 18 vectors and sequenced. The restriction and sequence mapping showed that most of T. evansi isolates belonged to the A1 and A2 types of Borst and to two new closely related types A3 and A4. A notable exception was RoTat 4/1 derived from a Sudanese stock which was found to display a characteristic brucei-like minicircle heterogeneity. The T. evansi minicircles analysed are not only homogeneous in sequence but also the region similar to the conserved region in Trypanosoma brucei and Trypanosoma equiperdum is flanked on its 5' end by a palindromic repeat of part of the conserved region. The highly conserved sequence GGGCGGT which appears to correspond to the initiation of synthesis of one of the Okazaki fragments contains an additional G and is located as in T. brucei and T. equiperdum about 73 bp 5' from the ORI. The nuclear DNA analysis confirms the kDNA study in that all the T. evansi stocks are members of a very homogeneous group in terms of sequence divergence. Moreover, our analysis also confirms that T. evansi is more closely related to the West African T. b. brucei and T. b. gambiense than to other African trypanosomes.