Comprehensive Identification and Functional Analysis of Fully Disordered Proteins Essential for Cell Survival

Proteins have traditionally been understood through their tertiary structures, with well-defined conformations considered essential for biological function. This classical structure-function paradigm implies that proteins with high intrinsic disorder would be less critical for cellular survival. However, recent discoveries have suggested that some intrinsically disordered proteins or even fully disordered proteins without any apparent tertiary structures are essential. Nevertheless, the biological significance of such disordered proteins is not comprehensively understood. Here, using genome-wide CRISPR screening, we demonstrated that highly or fully disordered proteins show comparable essentiality to well-folded proteins. Although structured proteins are more prevalent among essential genes, we found that the proportion of essential proteins is comparable across proteins of varying disorder levels. Focusing on FAM32A, one of the essential, fully disordered proteins identified in our screen, we show that its depletion leads to increased intron retention and downregulation of many other essential genes. These findings reshape our understanding of the structure-function paradigm, highlighting that fully disordered proteins can be essential for cellular viability. Overall design: RNA-seq profiles of wildtype HEK293T cells and their knockdown derivatives by siFAM32A, 24 hours after transfection. Total RNA and fractionated nuclear and cytoplasmic RNA samples were sequenced.