Nucleotide sequence organisation and analysis of the nuclear ribosomal DNA circle of the protozoan parasite Entamoeba histolytica

Devinder Sehgal, Vivek Mittal, Srinivasan Ramachandran, Suman K. Dhar, Alok Bhattacharya, Sudha Bhattacharya

Research output: Contribution to journalArticle

52 Scopus citations

Abstract

We have sequenced the extrachromosomal ribosomal DNA (rDNA) circle of the human protozoan parasite Entamoeba histolytica HM-1:IMSS and present here the complete sequence organisation of the 24.5-kb molecule. Each circle contains two 5.9-kb rDNA transcription units organised as inverted repeats. The regions downstream (3543 bp) and upstream (9216 bp) of the rDNAs contain various families of short tandem repeats. Some of the upstream repeats share extensive sequence homology with the downstream repeats. In addition to the rDNAs themselves, the rDNA circle appears to code for only one other transcript which is 0.7 kb in size as seen in Northern blots. From DNA sequence analysis, no open reading frame could be assigned to the transcript. Extrachromosomal rDNA circles also exist in other E. histolytica strains. Restriction enzyme maps of rDNA circle were constructed from E. histolytica strains 200:NIH, HK-9 and Rahman; and Entamoeba moshkovskii strain Laredo. Striking differences were observed in the organisation of some of them, e.g. the HK-9, Rahman and Laredo circles contained only one rDNA unit and lacked the 0.7-kb transcript sequence. The short repeat sequences upstream and downstream of rDNAs were present in HK-9 and Rahman but absent in Laredo. Circles with one rDNA unit may be derived from those with two units by homologous recombination at direct repeat sequences located upstream and downstream of the two rDNAs.

Original languageEnglish (US)
Pages (from-to)205-214
Number of pages10
JournalMolecular and Biochemical Parasitology
Volume67
Issue number2
DOIs
StatePublished - Oct 1994

Keywords

  • Entamoeba histolytica
  • Extrachromosomal
  • Intergenic spacer
  • rDNA circle
  • Repeated DNA

ASJC Scopus subject areas

  • Parasitology
  • Molecular Biology

Fingerprint Dive into the research topics of 'Nucleotide sequence organisation and analysis of the nuclear ribosomal DNA circle of the protozoan parasite Entamoeba histolytica'. Together they form a unique fingerprint.

Cite this