IDENTIFICATION OF ADDITIONAL RIBOSOMAL-RNA FRAGMENTS ENCODED BY THE PLASMODIUM-FALCIPARUM 6 KB ELEMENT

Sequences similar to mitochondrial large and small subunit rRNAs are f ound as small scattered fragments on a tandemly reiterated 6 kb elemen t in the human malaria parasite Plasmodium falciparum. The rDNA sequen ces previously identified include strongly conserved portions of rRNA, suggesting that fragmented rRNAs derived from them are able to associ ate into functional ribosomes. However, sequences corresponding to oth er expected rRNA regions were not found. We here report that 10 of the 13 previously described rDNA regions have abundant small transcripts. An additional 10 transcripts were found from regions not previously k nown to contain genes. Five of the latter have been identified as rRNA fragments, including those corresponding to the 5' end and 790 loop s equences of small subunit rRNA and the sarcin/ricin loop of large subu nit rRNA. Demonstration that most of the previously described rDNA reg ions have abundant transcripts and the identification of new transcrip ts with other portions of conventional rRNAs provide support for the h ypothesis that these small transcripts comprise functional rRNAs.