Cells from SDS patients are hypersensitive to actinomycin D in an SBDS-dependent manner. (A) Lymphoblasts from a healthy control, SDS patients (DF250, DF259, and SD101), and an RPS19⁺ DBA patient cell (CH106) were plated in the presence of increasing concentrations of actinomycin D. Cell viability was assayed after 72 hours. Assays were performed in triplicate per experiment and repeated for a minimum of 3 independent experiments. Bars represent the standard error. (B) DF259 cells were infected with lentivirus containing GFP alone or together with wild-type SBDS cDNA downstream of an IRES sequence. Lentiviral infection was greater than 90% as observed by fluorescence microscopy. Cell lysates were analyzed by immunoblotting with antibodies against SBDS and tubulin. (C) DF259 cells infected with lentivirus containing empty vector or full-length SBDS cDNA were plated in the presence of increasing concentrations of actinomycin D. Cell viability was assayed in triplicate per experiment and repeated for 3 independent experiments. Bars represent the standard error. (D) Lymphoblasts (normal control, DF259, and CH106) were plated in the presence of increasing concentrations of cycloheximide. Cell viability was assayed after 72 hours in triplicate for each experiment for a total of 3 independent experiments. Bars represent the standard error.