Two genes encoding unique proliferating-cell-nuclear-antigens are expressed in Toxoplasma gondii

Complete cDNA sequences encoding two novel proliferating-cell-nuclear-antig ens (designated TgPCNA1 and 2) were isolated fi om a Toxoplasma gondii tach yzoite cDNA library, and Southern analysis using cDNA probes confirmed the presence of two PCNA genes in T. gondii genomic DNA. Expressed-sequence-tag s were identified in the T. gondii database that matched each TgPCNA cDNA a nd closely related PCNA coding regions (designated PfPCNA1 and 2) were disc overed in sequence data obtained from chromosome 12 and 13 of Plasmodium fa lciparum. TgPCNA1 and PfPCNA1 were found to share the highest amino acid id entity at 49% compared to TgPCNA2 and PfPCNA2 (37% identity) whereas intras pecies PCNAs were determined to be less similar (27-30% identity). Phylogen etic analysis suggests the two apicomplexan PCNAs are the result of a gene duplication in the common ancestor of these parasites. Antibodies specific for TgPCNA1 (similar to 40 kDa) or TgPCNA2 (similar to 37 kDa) detected sin gle antigen species in tachyzoite extracts that were expressed at similar l evels in isolates representative of the T. gondii Type I, II and III strain s. TgPCNA1-specific cDNA probes detected multiple mRNA species on Northern blots, which when combined, were expressed 5-7 fold higher than the single species of mRNA detected by the TgPCNA2 probe. The difference in the number of mRNA species and comparative mRNA levels suggests each TgPCNA gene is i ndependently controlled, although in light of the nearly equal levels of pr otein a post-transcriptional mechanism may be responsible for equalizing pr otein expression. (C) 2000 Elsevier Science B.V. All rights reserved.