Ribosome RNA (rRNA) modifying enzymes are important factors in the assembly and function of ribosomes, dysregulation of which is frequently seen in human hematopoietic disorders. We only have limited knowledge of the catalytic role of rRNA modifying enzymes in the physiological and pathological processes of human hematopoiesis, although a few studies characterized the importance of rRNA modifications in these processes. Preliminary data (CRISPR screening) from my laboratory shows that the ablation of DIMT1 (an 18S rRNA N26,6A-dimethylation (N26,6A) methyltransferase) significantly impairs cell viability of hematopoietic stem progenitor cells (HSPCs). DIMT1 is highly expressed in HSPC, and its expression decreases in the differentiated lineages. However, the molecular function and detailed mechanism of DIMT1 in human hematopoiesis remain elusive. Even though DIMT1-mediated rRNA modifications are highly conserved, the catalytic activity of DIMT1 is dispensable for proper ribosome biogenesis. However, our recent results suggest that the catalytic activity of DIMT1 is required for the viability of HSPCs, while the catalytic-independent role of DIMT1 is important for 18S rRNA processing and ribosome biogenesis. This implies that DIMT1 may have a necessary role as a scaffold in ribosome biogenesis separate from its catalytic activity. Furthermore, we show that the catalytic role of DIMT1 is indispensable for the expression of genes involved in the Fanconi anemia and other DNA repair pathways. However, whether and how DIMT1-mediated N26,6A installation in 18S rRNA influences cell viability and DNA repair pathways in HSPCs are not known. Here, our goal is to understand the molecular function and the mechanistic details of the catalytic role of DIMT1 in the regulation of cell viability and gene expression in HSPCs. Specifically, Aim 1 will investigate the catalytic role of DIMT1 as an 18S rRNA methyltransferase in HSPC cell viability and protein synthesis. Aim 2 will investigate the molecular mechanism by which DIMT1- mediated N26,6A in 18S rRNA controls translation elongation using an in vitro eukaryotic translation system. Aim 3 will investigate the structure-function relationships and catalytic mechanism of DIMT1. Results from these studies will provide novel insights into how the catalytic role of DIMT1 impacts HSPC cell viability and the expression of genes Fanconi anemia and other DNA repair pathways. The understanding we will gain can be broadly applicable to hematopoietic studies and many other biological disciplines.