title: Extrachromosomal elements in the lower eukaryote Leishmania.
abstract: Extrachromosomal DNA elements have been identified in wild-type populations of the parasitic protozoan Leishmania. Elements from L. major and L. tropica were detected using orthogonal-field-alternation-gel electrophoresis. They are nonhomologous, supercoiled circular DNA molecules derived from different chromosomes in the Leishmania genome. Electron microscopy revealed that the elements have very similar physical properties; both are 80-kilobase supercoiled DNA molecules that contain large inverted repeat structures. The extrachromosomal DNAs are amplified in the Leishmania populations and show a fluctuation in copy number, from undetectable to around 20 copies per cell. After exposure of the L. tropica population to the drug methotrexate (MTX), a second amplified DNA was observed that is homologous to the extrachromosomal DNA found in L. major. Furthermore, wild-type Leishmania populations containing extrachromosomal DNA adapt more readily to MTX selection than populations with no amplified DNA. From these observations, there appears to be a relationship between the presence of extrachromosomal elements in wild-type Leishmania and the genesis and maintenance of MTX resistance in these organisms.
authors.affiliation: Department of Biochemistry and Biophysics, University of California, San Francisco 94143.
authors.forename: R C
authors.initials: RC
authors.lastname: Hightower
authors.forename: L M
authors.initials: LM
authors.lastname: Ruiz-Perez
authors.forename: M L
authors.initials: ML
authors.lastname: Wong
authors.forename: D V
authors.initials: DV
authors.lastname: Santi
mesh_terms: D000818:Animals; D002460:Cell Line; D005111:Extrachromosomal Inheritance; D005784:Gene Amplification; D007895:Leishmania tropica / Q000235:genetics*; D008727:Methotrexate / Q000494:pharmacology; D008854:Microscopy, Electron; D009710:Nucleotide Mapping
chemical_list: D008727:Methotrexate