Expression and Function of ASI2, a Gene Required for Sexual Reproduction in Tetrahymena Thermophila

Lihui Yin, Marquette University


Tetrahymena is a ciliated protozoan, with two functionally and structurally different nuclei, the micronucleus (Mic) and the macronucleus (Mac) (Karrer, 2000). The Mic, the germline nucleus, is diploid, and contains all of the DNA sequences of the genome in 5 chromosomes. It is transcriptionally silent during vegetative growth, and determines the genotype of sexual progeny. The Mac, the somatic nucleus, is pluriploid, and contains 85-90% of the Mic DNA sequences in about 220 chromosomes. It is transcriptionally active, and determines the phenotype of the cell. In the Mac genome, about 0.8% of the adenine residues are methylated to N6-methyladenine. However, in the Mic genome, there is no detectable N6-meA (Gorovsky et al., 1973; Yao and Gorovsky, 1974)...