It was recently proposed that excessive 5’-half-tRNAs were responsible for p53-dependent activation of cellular stress in mice (Hanada et al., 2013). Therefore, we hypothesized that inadequate CLP1 kinase activity might result in 3’-half-tRNAs that lacked a phospho group at the 5’-end (Figure 5A). We used a stress-induced viability assay to determine whether the patient mutation affected cell survival in the presence of various tRNA fragments, testing whether the addition of 3’- or 5’-half-tRNA fragments might exacerbate the HP-induced phenotype in human cells. We predicted that the substrate but not the product of CLP1 modification (i.e. the unphosphorylated but not the phosphorylated 3’-exon) would be toxic.
