The complete set of Toxoplasma gondii ribosomal protein genes contains two conserved promoter elements

Abstract

Recently we showed that de novo ribosome biosynthesis is transcriptionally regulated in Coccidia, depending on their life-cycle stage. Since the expression of ribosomal protein genes is likely coordinated, the transcriptional control of all Toxoplasma gondii ribosomal protein (RP) genes was analysed. Therefore, the complete set of all cytoplasmic RPs was defined, containing 79 different RPs in T. gondii. RP genes were randomly distributed over the genome, each with a unique upstream region with the exception of 8 RP genes which were paired in a head-to-head orientation. To study if the RP genes share conserved promoter elements, a database was made containing upstream sequences of all T. gondii RP genes. Promoter activity was confirmed for the upstream sequences of 8 RP genes, some of which are comparable in strength to the alpha-tubulin promoter. In the complete set of RP upstream sequences 2 novel and highly conserved elements were identified, named Toxoplasma Ribosomal Protein (TRP)-1 (consensus: TCGGCTTATATTCGG) and TRP-2 ([T/C]GCATGC[G/A]). TRP-1 and/or TRP-2 were present in 95% of all RP upstream sequences and moreover, were specifically localized in a small region near the presumptive transcriptional start site (10-330 bp upstream). Although TRP elements were mostly absent in known T. gondii promoters, they are present elsewhere in the T. gondii genome suggesting that they operate not only in RP genes but in a larger set of genes. The identification of TRP elements creates a basis to further study the underlying mechanism by which RP transcription is controlled in T. gondii.