We found that the level of normal histone transcripts decreased while that of polyadenylated ones increased upon PPP1R1A depletion (Supplementary Figure 2C), demonstrating that PPP1R1A is critical for cell cycle dependent normal histone gene transcription, and suggesting a compensatory mechanism which cancer cells utilize to cope with the loss of normal histone transcripts and to survive cell cycle arrest. Here, PPP1R1A is linked to cancer.