A specialized condensin complex participates in somatic nuclear maturation in Tetrahymena thermophila

Condensins are highly conserved proteins that are important for chromosome maintenance in nearly all forms of life. Although many organisms employ two forms of the condensin complex, the condensin genes in Tetrahymena have expanded even further. Here we report a form of condensin that is specifically active during sexual reproduction. This complex, condensin D, is composed of the core condensin proteins, Smc2 and Smc4, and two unique subunits, the kleisin Cph5 and Cpd2. Cpd2 is also found in somatic nuclei in vegetative cells, but is dispensable for growth and nuclear division. Immunoprecipitation experiments show that condensin D interacts with a putative member of a chromatin-remodeling complex during development. Condensin D is required for sexual reproduction and for endoreplication and genome reduction of the progeny’s somatic nuclei. Altogether, Tetrahymena possesses at least four forms of condensin to fulfill the needs of maintaining chromosomes in two different nuclei containing the somatic and germline genomes.