Expression of housekeeping genes during the asexual cell cycle of Plasmodium falciparum

In an earlier study, we found that calmodulin displayed an atypical expression for a housekeeping gene during the erythrocytic cycle of Plasmodium falciparum. The expression pattern was that of an inducible gene linked to the cell cycle, with a peak prior to replication, and not one of a gene that expresses itself in a constitutive way. In this work, we examined the expression pattern of other housekeeping genes, selecting genes from two functionally very different groups: those for three enzymes involved in carbohydrate metabolism--glucose-phosphate-isomerase (GPI), aldolase and glucose-6-phosphate-dehydrogenase (G6PD)--and for three proteins with structural and motor functions--actin-I, beta-tubulin and myosin. The mRNA of each gene was measured by reverse transcription-polymerase chain reaction in synchronic parasite samples that were 14, 28, 40 and 48 h old. GPI and G6PD achieved their maximum expression at 28 h, then declined, while aldolase increased its expression up to 40 h and remained high, but less so at 48 h. Actin and myosin showed the same pattern, increasing up to 48 h, while beta-tubulin expression peaked at 40 h. These findings confirm unconventional behavior in the expression of certain Plasmodium housekeeping genes and suggest the existence of different expression patterns for distinct functional groups.