The Abundant Polyadenylated Transcript 2 DNA Sequence of the Pathogenic Protozoan Parasite Entamoeba histolytica Represents a Nonautonomous Non-Long-Terminal-Repeat Retrotransposon- Like Element Which Is Absent in the Closely Related Nonpathogenic Species Entamoeba dispar

AUTOR(ES)

Willhoeft, Ute

FONTE

American Society for Microbiology

RESUMO

While comparing gene expression in the pathogenic organism Entamoeba histolytica and the closely related but nonpathogenic species Entamoeba dispar, we discovered that the E. histolytica abundant polyadenylated transcript 2 (ehapt2) and corresponding genomic copies are absent in E. dispar. Although polyadenylated, ehapt2 does not contain any overt open reading frame. Southern blot and sequence analyses revealed that about 500 copies of ehapt2 genomic elements were present in each cell and that the copies were distributed throughout the ameba genome. The various ehapt2 elements are regularly located in the vicinity of protein-encoding genes, downstream of pyrimidine-rich sequence stretches (40 to 125 bp; CT content, 79.2 to 85.5%), and are flanked by duplicated target sites of variable length. Target site duplications were obviously generated during integration of ehapt2 into the E. histolytica genome as one copy of the flanking repeat and the complete ehapt2 element are specifically absent in orthologous E. dispar genomic sequences. ehapt2 shares 3′ sequences with EhRLE, a recently identified non-long-terminal-repeat (non-LTR) retrotransposon-like element of E. histolytica, which contains a conceptual open reading frame for reverse transcriptase. Thus, ehapt2 has all of the properties of nonautonomous non-LTR retrotransposons. A comparison of various E. histolytica isolates suggested that transposition of ehapt2 takes place at a very low frequency as the genomic localization of ehapt2 elements was found to be well conserved. A mobile element such as ehapt2 could be a suitable mechanism to explain the infrequent and late transition of E. histolytica from a harmless gut commensal to an invasive pathogen.

Documentos Relacionados

• The site-specific ribosomal DNA insertion element R1Bm belongs to a class of non-long-terminal-repeat retrotransposons.
• Essential Motifs in the 3′ Untranslated Region Required for Retrotransposition and the Precise Start of Reverse Transcription in Non-Long-Terminal-Repeat Retrotransposon SART1
• Genomic DNA differences between pathogenic and nonpathogenic Entamoeba histolytica.
• DNA probes specific for Entamoeba histolytica possessing pathogenic and nonpathogenic zymodemes.
• Specific labeling of cysteine proteinases in pathogenic and nonpathogenic Entamoeba histolytica.