Sc 21758

HEK293T/17 were prepared as described above for RNA FISH. After the cells were permeabilized, the primary antibodies, anti-hnRNP K mouse monoclonal antibody [3C2]-ChIP Grade (ab39975, Abcam) and anti-PTBP1 mouse monoclonal antibody (32-4800, Thermo Fisher Scientific), were added and hybridized overnight. Alexa Fluor 647–conjugated goat anti-mouse IgG secondary antibodies (A-21236, Thermo Fisher Scientific) were used to visualize the results. Several organelle marker antibodies were tested as follows; anti-SC35 (S4045, Sigma-Aldrich), anti-nmt55/p54nrb (NONO, ab70335, Abcam), anti-ILF3 (ab133354, Abcam), anti-EF1A (sc-21758, SantaCruz), anti-ATP5 (mitochondria, ab14748, Abcam), anti-Calnexin (endoplasmic reticulum, ab202572, Abcam) and J2 monoclonal antibody (dsRNA, 10010200, SCICONS). MALAT1 probes labeled with Atto 633 (Supplementary Table S2).

Proximity ligation assays were performed in isolated neonatal rat or adult mouse cardiomyocytes using the Duolink In Situ Kit (Olink Bioscience) according to the manufacturer's instructions. Cells were either stained for anti‐TIP30 (#ab177961, Abcam, 1:100) and anti‐eEF1A1 (#sc‐21758, Santa Cruz, 1:100) or anti‐eEF1A1 (#ab118703, Abcam, 1:100) and anti‐eEF1B2 (#ab77043, Abcam, 1:100). Control cells were stained for anti‐TIP30 (#ab177961, Abcam, 1:100) and anti‐Myc (#2276, Cell Signaling, 1:100).