Component of the kinetochore which plays a role in stabilizing microtubules and so allowing accurate chromosome segregation. Has a role in the RNA interference (RNAi) pathway which is important for heterochromatin formation and accurate chromosome segregation. A member of the RNA-induced transcriptional silencing (RITS) complex which is involved in the biosynthesis of dsRNA from primer siRNAs provided by the RNA-directed RNA polymerase (RDRC) complex. Ago1, chp1 and tas3 interact to form the core of the RNA-induced transcriptional silencing (RITS) complex. The RITS complex interacts with the RDRC complex via interaction between ago1 and hrr1. Clr4 has a role in mediating this interaction (PubMed:14704433). Interacts with dri1 (PubMed:33693625). Associates with telomeric and mating-type region heterochromatin (PubMed:15607976).