A role for poly(dA)poly(dT) tracts in directing activity of the Plasmodium falciparum calmodulin gene promoter

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Hannah E J Polson1, Michael J Blackman

  • 1Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, UK.

Molecular and Biochemical Parasitology
|April 27, 2005
PubMed

Insights

This study maps transcription start sites for Plasmodium falciparum calmodulin (pfcam) and STI1 genes. Poly(dA)poly(dT) tracts appear crucial for regulating pfcam gene transcription initiation.

Area of Science:

  • Molecular Parasitology
  • Gene Regulation
  • Plasmodium falciparum Biology

Background:

  • The Plasmodium falciparum calmodulin (pfcam) gene is developmentally regulated during the blood-stage cycle.
  • The pfcam promoter is located within intergenic DNA separating it from an upstream gene encoding a co-chaperone STI1 homolog.
  • Understanding gene regulation is critical for targeting malaria parasites.

Purpose of the Study:

  • To map the transcription-initiation sites of the Plasmodium falciparum calmodulin (pfcam) and pfSTI1 genes.
  • To identify regulatory elements within the intergenic promoter regions.
  • To investigate the role of poly(dA)poly(dT) tracts in transcription initiation.

Main Methods:

  • Oligo-capping method to selectively capture full-length, capped transcripts.
  • Deletion analysis of the pfcam promoter to assess activity.
  • Electromobility-shift assays (EMSA) to study nuclear factor binding.

Main Results:

  • Multiple transcription-initiation sites were identified for both pfSTI1 and pfcam genes.
  • pfcam transcripts exhibited varying 5' untranslated region (UTR) lengths (3-173 nucleotides), with longer UTRs showing preferential splicing.
  • Nuclear factor binding to promoter probes correlated with poly(dA)poly(dT) tract density and could be inhibited by poly(dA)poly(dT).

Conclusions:

  • The basal pfcam promoter is located between approximately -300 and -230 bp upstream of the open reading frame (ORF).
  • Transcription initiation in P. falciparum shows low sequence specificity but preferentially occurs downstream of long poly(dA)poly(dT) tracts.
  • Poly(dA)poly(dT) tracts are significant regulatory elements in Plasmodium falciparum gene expression.

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