Entamoeba histolytica ribosomal RNA genes are carried on palindromic circular DNA molecules

Marion Huber, Barbara Koller, Carlos Gitler, David Mirelman, Michel Revel, Shmuel Rozenblatt, Leonard Garfinkel

Research output: Contribution to journalArticlepeer-review

Abstract

Highly abundant DNA fragments obtained after restriction enzyme digests of nuclear DNA of Entamoeba histolytica strain HM-1:IMSS have been cloned and characterized. Northern blot hybridization to E. histolytica rRNA and sequence analysis identified the abundant DNAs as ribosomal DNA containing species. Several overlapping clones containing these abundant DNAs were isolated from 4 different genomic libraries of E. histolytica. Alignment of the restriction maps was consistent with a circular molecule, about 24.6 kilobase pairs (kb) in size. Nuclease BA131 digestion provided additional evidence for the circular nature of this DNA. The ribosomal DNA molecule contains two large inverted repeat-regions, each at least 5.2 kb in length. Sequence analysis of clone R715 revealed homology to the large rRNA units of various eukaryotic organisms. This clone was located in both inverted repeats, suggesting two rRNA cistrons per molecule. The inverted repeats are flanked by stretches of DNA which contain tandemly reiterated sequences. Southern blot analysis of E. histolytica nuclear DNA revealed the presence of two populations of molecules. These molecules have identical arrangements of restriction sites, but differ in size (0.7 kb) in a fragment containing tandemly reiterated sequences. Analysis of E. histolytica nuclear DNA by electron microscopy also revealed circular molecules. These molecules are about 26.6 kb ± 0.5 kb in size and contain structural features predicted by the restriction map of the extra-chromosomal ribosomal DNA of E. histolytica.

Original languageEnglish
Pages (from-to)285-296
Number of pages12
JournalMolecular and Biochemical Parasitology
Volume32
Issue number2-3
DOIs
StatePublished - 15 Jan 1989
Externally publishedYes

Keywords

  • 25S rDNA sequence
  • Circular episome
  • Electron microscopy
  • Entamoeba histolytica
  • rDNA organization

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