Nucleic Acids Research, 2006, Vol. 34, No. 2 501 Figure 2. Organization of selenoprotein genes in P.falciparum. Exon–intron structure of the four selenoprotein genes is shown with exons indicated by boxes and introns by lines connecting the exons. The location of ORFs and SECIS elements is indicated by filled boxes, and the untranslated regions (other than SECIS elements) by open boxes. The location of initiator ATG codons, Sec-encoding TGA codons, stop codons and SECIS elements is indicated by black arrows. Numbers below the sequences illustrate exon–intron junctions and correspond to nucleotides in P.falciparum contigs from PlasmoDB. Red arrows indicate location and orientation of primers, which were used to verify gene expression and examine organization of selenoprotein genes. monitor Sec insertion into proteins and to characterize the dependence of Sec insertion on SECIS elements (17,19). We prepared two GFP fusion expression constructs which were designed to test whether Plasmodium SECIS element support Sec insertion into Plasmodium and mammalian selenoproteins. In the ﬁrst construct (Figure 4A, #3), a coding region of P.falciparum Sel1 was placed downstream of GFP and followed with the entire Sel1 30-UTR including a SECIS element. The second construct contained a coding region of mouse SelH fused to GFP and also had a Sel4 30-UTR includ- ing a SECIS element (Figure 4A, #2). These constructs, as well as GFP-SelH with a SelH SECIS element (positive control) and GFP alone (negative control) constructs, were transfected into mouse NIH 3T3 cells and