Transcriptional mapping and RNA processing of the Plasmodium falciparum mitochondrial mRNAs

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.