MAPPING THE GERM-LINE AND SOMATIC GENOMES OF A CILIATED PROTOZOAN, TETRAHYMENA-THERMOPHILA

Ciliates are among the very few eukaryotes in which the powers of mole cular biology, conventional genetics, and microbial methodology can be synergistically combined. Because ciliates also are distant relatives of vertebrates, fungi, and plants, the sequencing of a ciliate genome wilt be of import to our understanding of eukaryotic biology. Tetrahy mena thermophila is the only ciliate in which a systematic genetic map ping of DNA polymorphisms has begun. Tetrahymena has many biological f eatures that make it a specially or uniquely useful experimental syste m for fundamental research in cell and molecular biology and for biote chnological applications. A key factor in the usefulness of Tetrahymen a is the speed, facility, and versatility with which it can be cultiva ted under a wide range of nutrient conditions, temperature, and scale. This article describes the progress made in genetically and physicall y mapping the genomes of T. thermophila: the micronuclear (germ-line) genome, which is not transcriptionally expressed, and the macronuclear (somatic) fragmented genome, which is actively expressed and determin es the cell's phenotype.