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Mol. Cell. Biol., Feb 1997, 604-611, Vol 17, No. 2
R Hernandez-Rivas, D Mattei, Y Sterkers, DS Peterson, TE Wellems and A Scherf
The antigenic variation and cytoadherence of Plasmodium falciparum-
infected erythrocytes are modulated by a family of variant surface proteins
encoded by the var multigene family. The var genes occur on multiple
chromosomes, often in clusters, and 50 to 150 genes are estimated to be
present in the haploid parasite genome. Transcripts from var genes have
been previously mapped to internal chromosome positions, but the generality
of such assignments and the expression sites and mechanisms that control
switches of var gene expression are still in early stages of investigation.
Here we describe investigations of closely related var genes that occur in
association with repetitive elements near the telomeres of P. falciparum
chromosomes. DNA sequence analysis of one of these genes (FCR3-varT11-1)
shows the characteristic two-exon structure encoding expected var features,
including three variable Duffy binding-like (DBL) domains, a transmembrane
sequence, and a carboxy-terminal segment thought to anchor the protein
product in knobs at the surface of the parasitized erythrocyte.
FCR3-varT11-1 cross-hybridizes with var genes located close to the
telomeres of many other P. falciparum chromosomes, including a transcribed
gene (FCR3- varT3-1) in chromosome 3 of the P. falciparum FCR3 line. The
relatively high level transcription from this gene shows that the
polymorphic chromosome ends of P. falciparum, which have been proposed to
be transcriptionally silent, can be active expression sites for var genes.
The pattern of the FCR3-varT11-1 and FCR3-varT3-1 genes are variable
between different P. falciparum lines, presumably due to DNA
rearrangements. Thus, recombination events in subtelomeric DNA may have a
role in the expression of novel var forms.
Copyright © 1997, American Society for Microbiology
Expressed var genes are found in Plasmodium falciparum subtelomeric regions
Unite de Parasitologie Experimentale, CNRS URA 1960, Institut Pasteur, Paris, France.
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