(A) Schematic representation of DsRed-fused TnT3 COOH-terminus mutant with the KLKRQK sequence retained (TnCT-KL/DsRed) or removed (TnCT-YD/DsRed). (B) C2C12 cells expressing the deletion constructs. TnCT-KL/DsRed is localized exclusively in the nucleus with an enriched nucleolar area. In contrast, TnCT-YD/DsRed is present throughout the cell, with marked reduction in nucleolar enrichment. Nuclei (blue, Hoechst 33342), TnT3-DsRed fusion protein (red). Scale bar, 50 µm. (C) The Tnnt3 KLKRQK sequence is conserved across mammalian species.