
Low expression of U1 snRNAs from endogenous loci in human cell lines. Expression levels of snRNAs were measured by RT-qPCR. The expression values for vU1s were calculated relative to the canonical U1 snRNA and normalized to the U2 snRNA (n = 3) in HeLa, HEK293T, K562, MV-4-11, and TF-1a cells. vU1A6* was not tested in HEK293T cells. Sequences of primer sets used for RT-qPCR are provided in Supplemental Table S2.










