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Analysis of Single-cell Gene Transcription by RNA Fluorescent In Situ Hybridization (FISH)
Published on: October 7, 2012
Transcriptional mapping and RNA processing of the Plasmodium falciparum mitochondrial mRNAs
D H Rehkopf1, D E Gillespie, M I Harrell
1Seattle Biomedical Research Institute, WA 98109-1651, USA.
Abstract:
The mitochondrial genome of Plasmodium falciparum encodes three protein coding genes and highly fragmented rRNAs. The genome is polycistronically transcribed and, since gene-size transcripts are much more abundant than the polycistronic transcripts, the latter are presumably cleaved to produce the smaller, mature mRNAs and rRNAs. Mapping the transcripts of the P. falciparum mitochondrial protein coding genes shows that the 3' end of each gene directly abuts the 5' end of the gene located immediately downstream. The 5' ends of the protein coding genes are also closely apposed to adjacent genes, with one directly abutting a gene on the same DNA strand and two others separated by just 13 nt from an rDNA fragment encoded on the opposite strand. These mapping data are consistent with production of the mRNAs by cleavage from a polycistronic precursor transcript. Further processing of the mRNAs comes from addition of oligo(A) tails. Unexpectedly, the presence and length of such tails varies in a gene-specific fashion. In this regard, polyadenylation of the P. falciparum mitochondrial mRNAs is more similar to that seen for the P. falciparum mitochondrial rRNAs than that of mitochondrial mRNAs in other organisms.
Insights
The Plasmodium falciparum mitochondrial genome produces mRNA through polycistronic transcription and subsequent cleavage. Unexpectedly, mRNA processing involves gene-specific oligo(A) tail addition, similar to rRNA processing.
Area of Science:
- Molecular Biology
- Genetics
- Parasitology
Background:
- The Plasmodium falciparum mitochondrial genome is compact, encoding few proteins and fragmented rRNAs.
- Mitochondrial gene expression in P. falciparum is known to be polycistronic.
Purpose of the Study:
- To investigate the transcriptional organization and mRNA processing of the P. falciparum mitochondrial genome.
- To elucidate the mechanisms of mRNA maturation, including polyadenylation.
Main Methods:
- Transcript mapping of P. falciparum mitochondrial protein-coding genes.
- Analysis of transcript termini and processing intermediates.
Main Results:
- Transcript mapping confirms polycistronic transcription with genes arranged in a head-to-tail manner.
- Mature mRNAs are likely generated by cleavage of polycistronic precursors.
- Oligo(A) tail addition to mRNAs is observed, with significant gene-specific variation in tail presence and length.
- Polyadenylation patterns of mitochondrial mRNAs resemble those of mitochondrial rRNAs more than those in other organisms.
Conclusions:
- The P. falciparum mitochondrial genome utilizes polycistronic transcription followed by precise cleavage for mRNA production.
- Gene-specific oligo(A) tailing represents a unique post-transcriptional modification mechanism in P. falciparum mitochondria.
- This unusual polyadenylation strategy highlights distinct regulatory mechanisms in malaria parasite mitochondrial gene expression.
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