SRSF3 and SRSF4 bind to numerous intronless histone mRNAs at a consistent position. (a) SRSF3 and SRSF4 CLIP-tags and clusters in HIST2H2BB and HIST1H2AB genes. Labels as in Figure 1a. The orange arrowheads mark the mRNA 3' end cleavage site. (b) Mapping of SRSF3 (left panel) and SRSF4 (right panel) crosslink sites to the ORF-3' UTR boundary of histone mRNAs. The position 0 marked with a dotted line represents the ORF-3' UTR boundary. (c) Cytoplasmic levels of histone mRNAs associated with SRSF3 or SRSF4 determined by UV-RNA immunoprecipitation and reverse transcription quantitative PCR. To prime the reverse transcription reactions, hexamers were used to detect total and oligo-dT to detect polyadenylated histone mRNAs. Data are presented relative to the input sample. Mock is the non-immune control. *P < 0.05, **P < 0.01, ***P < 0.001 (Student's unpaired t-test, n = 3-6). Error bars are standard deviation. IP, immunoprecipitation.