Identification and characterization of the genes for two topoisomerase I-interacting proteins from Saccharomyces cerevisiae.

The two-hybrid system was used to identify yeast genes encoding proteins that interact with DNA topoisomerase I. Two new genes were found and named TOF1 and TOF2. The Tof1 protein has 1238 amino acids and no obvious homologues in databases. The Tof2 protein has 771 amino acids; it is quite closely related to another yeast protein, the product of an uncharacterized ORF. Both tof1 and tof2 null mutants, and tof1-tof2 double mutants, grow normally and have normal levels of topoisomerase I activity. TOF2 shows various genetic interactions with TOP1 and HPR1. The implications of these interactions for TOF2 function are discussed.