Required for G1 arrest and mating in response to nitrogen starvation. Ago1 regulation of cytokinesis and cell cycle checkpoints occurs downstream of dcr1. Required, indirectly, for regulated hyperphosphorylation of cdc2. Has a role in the RNA interference (RNAi) pathway which is important for heterochromatin formation, accurate chromosome segregation, centromere cohesion and telomere function during mitosis and meiosis. Required for silencing at the centromeres and for initiation of transcriptionally silent heterochromatin at the mating type locus. Promotes histone H3K9 methylation necessary for centromere function. Required for recruitment of swi6 and cohesin to an ectopic dg repeat. 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. Has ribonuclease H-like cleavage (slicing) activity towards target messages complementary to siRNA and can direct site-specific cleavage of RNA substrates via siRNA. Slicing activity is required for both post-transcriptional and transcriptional gene silencing as well as for histone H3 'Lys-10' methylation spreading, conversion of double-stranded siRNA to single-stranded siRNA and siRNA-dependent association of ago1 with chromatin. A member of the argonaute siRNA chaperone (ARC) complex which is required for histone H3K9 methylation, heterochromatin assembly and siRNA generation. The ARC complex contains mostly double-stranded siRNA. 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. Component of the argonaute siRNA chaperone (ARC) complex composed of ago1, arb1 and arb2. Interacts with arb1. Associates with telomeric and mating-type region heterochromatin. Belongs to the argonaute family. Ago subfamily.