Plays an essential role in growth and, with Dicer, also involved in microRNA (miRNA)-mediated translational repression. The RNA interference pathway is implicated in antigenic variation having a role in regulation of variant-specific surface protein (VSP)-coding gene expression. Several VSP genes are transcribed but only transcripts encoding the VSP to be expressed accumulate. Antisense RNAs corresponding to the silenced VSP genes are detected (By similarity). Interacts with miR2. Highly specific binding to the mRNA m7G-cap. May be a component of the RNA-induced silencing complex (RISC), a sequence-specific, multicomponent nuclease that destroys or silences messenger RNAs homologous to the silencing trigger (By similarity). PAZ domain is absent, but Ago is capable of binding small RNAs in the same way as the other Argonaute proteins. Belongs to the argonaute family. Ago subfamily.