Characterization of a conserved extrachromosomal element isolated from the avian malarial parasite Plasmodium gallinaceum.

Abstract

We have identified a conserved, repeated, and highly transcribed DNA element from the avian malarial parasite Plasmodium gallinaceum. The element produced multiple transcripts in both zygotes and asexual blood stages of this parasite. It was found to be highly conserved in all of five malarial species tested and hybridized at reduced stringency to other members of the phylum Apicomplexa, including the genera Babesia, Eimeria, Toxoplasma, and Theileria. The copy number of the element was about 15, and it had a circularly permuted restriction map with a repeat unit length of about 6.2 kilobases. It could be separated from the main genomic DNA by using sucrose gradients and agarose gels, and it migrated separately from the recognized Plasmodium chromosomes on pulse-field gels. In the accompanying paper

Extrachromosomal DNA in the Apicomplexa

“…VOL. 61,1997 EXTRACHROMOSOMAL DNA IN THE APICOMPLEXAConservation Snap-back and cross-hybridization experiments with fragments from the IR of the malarial circle provided evidence for conservation of the rDNA palindrome in two other genera of apicomplexans, namely, T. gondii and Eimeria tenella (122). These observations confirmed the suggestion of Borst et al (10) that the cruciform structure they observed in T. gondii circular DNA by electron microscopy was derived from palindromic rRNA genes.…”

“…There is evidence that malaria parasites carry at least one DNA polymerase resembling DNA polymerase ␥ in its drug sensitivities (14), and in vitro an aphidicolin-resistant VOL. 61,1997 EXTRACHROMOSOMAL DNA IN THE APICOMPLEXAenzyme was shown to be highly sensitive to the nucleotide analog (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine (HPMPA) (99). However, although HPMPA effectively arrested parasites in schizogony, the replication of both the organelle DNAs in vivo was unaffected by the inhibitor, so it is not clear if the same polymerase is responsible for replication of either of the organelle DNAs.…”

“…A radioactive probe made from the mtDNA of P. gallinaceum detected a fragment of around 7 kb in HindIIIdigested genomic DNA of Babesia microti (61). It is possible that this was the counterpart of the multicopy 9-and 7.4-kb molecules recorded in undigested genomic DNA of different Babesia species (59,94).…”

“…Despite this, all the known functional domains of the protein are readily recognized in the predicted malarial peptide, which resembles the plastid type much more than it resembles the bacterial type ( VOL. 61,1997 EXTRACHROMOSOMAL DNA IN THE APICOMPLEXApurea (89a) but unlike in most higher plants, the malarial rpoC 1 gene does not have an intron. An intergenic region of 11 nt separates rpoC 1 from rpoC 2 , which codes for the largest subunit of the chloroplast-encoded RNA polymerase.…”

Unidirectional dominance of cytoplasmic inheritance in two genetic crosses of Plasmodium falciparum.

“…Between these species, the 6-kb DNA molecule is conserved in both organization and sequence (1,19,20,39). Figure 6 shows that purified P. gallinaceum male gametes have substantially less 6-and 35-kb DNAs than do the female gametes.…”