CODON USAGE IN CRYPTOSPORIDIUM-PARVUM DIFFERS FROM THAT IN OTHER EIMERIORINA

Codon usage of Crytosporidium parvum was compared with those of other Eimeriorina Toxoplasma gondii and Eimeria tenella and revealed a biase d use of synonymous codons with a preference for NNU (40.0%) and NNA ( 33.4%). There was no close resemblance of the codon usage of C. parvum to T. gondii (correlation coefficient, r = 0.14) or E. tenella (r = 0 .14) but it was similar to Entamoeba histolytica (r = 0.75) and Plasmo dium falciparum (r = 0.5). Analysis of the codon usage in homologous g ene sequences (actin, P-tubulin) also failed to reveal a close relatio nship between C. parvum and T. gondii or E. tenella. The low usage cod ons in C. parvum were most frequently used codons in T. gondii and E. tenella. These observations are consistent with 18S rRNA sequence anal ysis which shows no close relationship of Cryptosporidium with other E imeriorina (Sarcocystis, Toxoplasma and Eimeria) and questions the val idity of the current classification of C. parvum.