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Centrins are highly conserved, ubiquitous cytoskeletal components which belong to the EF-hand superfamily of Ca2+-modulated proteins. We report here the molecular characterization of new members of the centrin family, Paramecium centrins. Previous studies described the organization of the infraciliary lattice (ICL), the innermost cortical cytoskeletal network of Paramecium, and showed that it was composed of a set of low-molecular-mass, Ca2+-binding polypeptides [Garreau de Loubresse, N., Klotz, C., Vigues, B., Rutin, J & Beisson, J. (1991) Biol. Cell 71, 217-225]. In this paper we show that these polypeptides are recognized by specific anti-centrin polyclonal antibodies. Their microsequences revealed four distinct N-termini. For one of them, ICL1, N-terminal and internal peptide sequences were used for PCR amplification and cloning of a DNA fragment containing a complete centrin coding sequence. The deduced amino acid sequence presents about 50% identify with those of centrins from other species. Further molecular analysis allowed us to identify two additional closely related, co-expressed ICL1 genes, providing the first example of a centrin multigenic family in a microorganism. [ABSTRACT FROM AUTHOR]