Cell cycle dependent episomal expression of Renilla luciferase from HBIRH with two different var intron promoters. A: Diagram of bidirectional expression construct pHBIRH. The construct contains the intron from either PFC0005w or PFD0020c, resulting in total plasmid sizes of 6380 bp or 6432 bp, respectively. bsd: blasticidin-S-deaminase gene; 3': 3'untranslated region of Pfhrp2; Renilla: Renilla luciferase gene; intron: intron var gene containing bi-directional promoter activity. B: Luciferase activity was measured from P. falciparum NF54 parasites stably transformed with pHBIRH containing either var intron PFC0005w (grey) or var intron PFD0020c (black) as a bidirectional promoter. Samples were taken at different time points throughout intra-eryhtrocytic cycle: 16 h (ring), 32 h (troph) and 40 hours (schizont) post-invasion. Samples were measured in triplicate and error bars indicate the standard deviation.