Genomic distribution and functional characterisation of two distinct and conserved Plasmodium falciparum var gene 5 ' flanking sequences

Approximately 50 highly diverse var genes distributed throughout the haploi d genome of the malaria parasite Plasmodium falciparum code for PfEMP1 vari ants located on the surface of infected erythrocytes. PfEMP1 is involved in cytoadherence of parasitised red blood cells and undergoes antigenic varia tion through differential expression of var genes. Members of the var gene family are located in chromosome-internal positions on chromosomes 4, 7, 8 and 12, and in subtelomeric regions of all chromosomes. Here we show that t here are two distinct and conserved types of 5' upstream regions (var 17-ty pe and 5B1-type) of mi genes, and suggest that most subtelomeric var genes are flanked by a var 17-type 5' upstream sequence. In contrast, 5B1-type 5' upstream are localised to chromosomes that have been shown to contain var genes within chromosome-internal regions. Transcriptional analysis using RT -PCR revealed that var genes flanked by either type of 5' upstream sequence are transcribed in in vitro cultured trophozoite stage parasites. In addit ion, we have shown that the 5' flanking sequences of four different var gen es are able to drive transient expression of the cat reporter gene. Our res ults suggest that at least the minimal regulatory sequences required for tr anscription of var genes are conserved among both subgroups of the cai gene family. Furthermore, these sequences provide new markers for the investiga tion of the chromosomal organisation of cai genes. (C) 2000 Elsevier Scienc e B.V. All rights reserved.