Phylogenetic position and codon usage of two centrin genes from the rumen ciliate protozoan, Entodinium caudatum

A lambda phage cDNA expression library was constructed from washed suspensions of the rumen ciliate protozoan, Entodinium caudatum, which had been maintained in an isolated, monofaunated sheep. The library was screened using an anti-E. caudatum antiserum raised in rabbits against sonically disrupted protozoa, DNA sequences for two centrins or caltractins, a subfamily of the EF-hand Ca(2+)-modulated proteins which are closely related, highly conserved cytoskeletal proteins, were identified and characterised. Their phylogenetic position was established relative to other centrin gene sequences. The two proteins showed homology to Paramecium tetraurelia centrins: 50 and 52% identities and 71 and 75% similarities in the protein sequence, over 99 and 110 amino acids fragments. Codon usage and indices revealed the E. caudatum follows universal codon usage, but with a restricted number of codons, and has a low G&C content.