Part of the ribosome quality control system (RQC). Recruits Ala-charged tRNA and directs the elongation of stalled nascent chains on 50S ribosomal subunits, leading to non-templated C-terminal Ala extensions (Ala tail). The Ala tail promotes nascent chain degradation. Selectively binds tRNA(Ala)(UGC), which is presumably the sole source of tRNA(Ala) used for Ala tailing directed by this protein. May add between 1 and at least 8 Ala residues; detection of the Ala tail requires either deletion of clpP or its inhibition. Binds to 50S ribosomal subunits, at least 30% of which contain a P-site tRNA and thus are obstructed. Associates with stalled 50S ribosomal subunits. Highly expressed during stationary phase. Up-regulated under secretion stress conditions, possibly in a CssR/CssS-dependent manner. Not essential in rich media; synthetic growth defects are seen in double rqcH ssrA mutants, further exacerbated by translational inhibitors spectinomycin and erythromycin or at elevated temperatures. Decreased accumulation of a stalled reporter protein. Triple rqcH clpP ssrA mutants cannot be generated. Activity of this protein is best tested in a clpP or ssrA deletion mutant; ssrA (tmRNA) encodes the SsrA tag added to nascent proteins in stalled ribosomes by trans-translation, which targets the nascent protein for degradation. Belongs to the NEMF family. Extended N-terminus. Extended N-terminus. Extended N-terminus.