ASC1 and RPS3: new actors in 18S nonfunctional rRNA decay

Proposed model depicting the contributions of multiple independent targeting and decay pathways to 18S NRD. A stalled ribosome harboring mutant 18S rRNA (blue splatter) can be marked for decay by two separate pathways involving either Asc1p or Dom34p:Hbs1p. Once marked (possibly by covalent modification of the Rps3p C-terminal tail), 40S ribosomes are disassembled and 18S rRNA degraded by 5′ → 3′ and 3′ → 5′ decay pathways.