SRP230665 PRJNA590617 PASTMUS: mapping functional elements at single amino acid resolution in human cells Identification of functional elements for a protein of interest is important for achieving a mechanistic understanding. However, it remains cumbersome to assess each and every amino acid of a given protein in relevance to its functional significance. Here, we report a strategy, PArsing fragmented DNA Sequences from CRISPR Tiling Mutagenesis Screening (PASTMUS), which provides a streamlined workflow and a bioinformatics pipeline to identify critical amino acids of proteins in their native biological contexts. Using this approach, we map six proteins - three bacterial toxin receptors and three cancer drug targets, and acquire their corresponding functional maps at amino acid resolution.