Epitope tags are not created equal: Disruption of cellular function of a translation factor by a short viral tag.

Cellular identity and fate are determined by the proteins synthesized. Initiation of mRNA translation requires an important translation factor, eIF4G ( in ). Embryos use mRNA translational control for spatial and temporal regulation of protein synthesis. Using CRISPR engineering, we added in-frame epitope and fluorescent tags (V5, Myc, Flag, GFP, and mCherry) to IFG-1 . Tagged forms containing the V5 epitope caused embryonic arrest. Internal disruption of the V5 tag restored viability at 25°C. This study demonstrates that the molecular nature of a small epitope tag is sufficient to disrupt embryogenesis.