COMPOSITIONAL PROPERTIES OF NUCLEAR GENES FROM PLASMODIUM-FALCIPARUM

We have analyzed the compositional distributions of coding sequences a nd their different codon positions, as well as the codon usage of the nuclear genes of Plasmodium falciparum, a parasite characterized by an extremely CC-poor genome. As expected, coding sequences are AT-rich, codon usage is strongly biased towards A or T in third codon positions , and some particular amino acids (aa) are especially abundant in the encoded proteins. Remarkably, however, no difference was detected betw een housekeeping (HK) and antigen (Ag) genes, in spite of differences in expression level and evolutionary constraints. Moreover, all the fe atures found in P. falciparum are very similar to those found in a bac terium characterized by a very GC-poor genome, Staphylococcus aureus. These findings stress the importance of compositional constraints in d etermining codon usage and aa utilisation.