Unresolved stalled ribosome complexes restrict cycle progression after genotoxic stress

Translation of damaged mRNA can lead to ribosome stalling, thereby producing incomplete proteins toxic to the cell. The mechanism of ribosome-associated quality control (RQC) disassembles stalled ribosomes through the actions of the ASC-1 complex (ASCC). Here, we show that some reagents that chemically damage RNA, such as ultraviolet light (UV), cause ribosome stalling, which leads to accumulation of the ASC-1 complex (ASCC) on stalled ribosomes and stable interaction of the ASCC3 helicase with RNA. In contrast, the ASCC was not similarly affected by emetine or anisomycin-induced ribosome stalling. Our work identified two different types of stalled ribosome. Ribosomes arrested by emetine or anisomycin are transient as they are resolved by the ASCC. Whereas the ASCC fails to split some stalled ribosomes, such as those induced by UV, resulting in long-lived stalled ribosome complexes. We show that ribosome stalling activates the G1/S and G2/M cell cycle checkpoints with long-lived stalled ribosomes causing prolonged checkpoint activation. Thus, the cell adjusts this adaptive survival response to match the nature of the stalled ribosome.