GENOME DOWNSIZING DURING CILIATE DEVELOPMENT - NUCLEAR DIVISION-OF-LABOR THROUGH CHROMOSOME RESTRUCTURING

The ciliated protozoa divide the labor of germline and somatic genetic functions between two distinct nuclei. The development of the somatic (macro-) nucleus from the germinal (micro-) nucleus occurs during sex ual reproduction and involves large-scale, genetic reorganization incl uding site-specific chromosome breakage and DNA deletion. This intrigu ing process has been extensively studied in Tetrahymena thermophila. C haracterization of cis-acting sequences, putative protein factors, and possible reaction intermediates has begun to shed light on the underl ying mechanisms of genome rearrangement. This article summarizes the c urrent understanding of this phenomenon and discusses its origin and b iological function. We postulate that ciliate nuclear restructuring se rves to segregate the two essential functions of chromosomes: the tran smission and expression of genetic information.