Required for 40S ribosome biogenesis. Involved in nucleolar processing of pre-18S ribosomal RNA and ribosome assembly. Essential for vegetative growth (By similarity). Component of the ribosomal small subunit (SSU) processome composed of at least 40 protein subunits and snoRNA U3. Interacts with snoRNA U3. Interacts with MPP10, KRI1 and with ribosomal proteins RPS1A, RPS4A, RPS4B, RPS8A, RPS8B, RPS11A, RPS11B, RPS13, RPS24, RPS25, RPL4A, RPL7B, RPL8, RPL23, RPL25 and RPL28 (By similarity). Belongs to the KRR1 family.