Required for progression through the G1 and S phases of the cell cycle and for S phase entry. Activates transcription of the histone H2A, histone H2B, histone H3 and histone H4 genes in conjunction with MIZF. Also positively regulates the ATM, MIZF and PRKDC promoters. Transcriptional activation may be accomplished at least in part by the recruitment of the NuA4 histone acetyltransferase (HAT) complex to target gene promoters. Interacts with the cylin/CDK complexes CCNE1/CDK2 and CCNA1/CDK2. Interacts with BZW1, CASP8AP2, CREBBP, MIZF and YY1. Interacts with the RUVBL1, RUVBL2 and TRRAP subunits of the NuA4 complex. May also interact with GAPDH, NME1, NME2 and STIP1. Concentrates in two Cajal bodies tethered to histone gene clusters at chromosome 6p21 during G1, S and G2 phases. Also concentrates in two additional Cajal bodies tethered to histone gene clusters at chromosome 1q21 specifically during S and G2 phases. Ubiquitously expressed. Expressed throughout the cell cycle. Expression peaks at the G1/S phase boundary and declines during S phase. By expression of E2F1, E2F2, E2F3 and E2F4. Expression is reduced in response to radiation-induced DNA damage. The LisH domain is required for the activation of histone gene transcription. Phosphorylated at Ser-775, Ser-779, Ser-1100, Thr-1270 and Thr-1350 by CCNE1/CDK2 at G1-S transition and until prophase, which promotes association with histone gene clusters and stimulates activation of histone transcription. Also phosphorylated by CCNA1/CDK2 in vitro. Belongs to the NPAT family. Chimeric cDNA. A chimeric cDNA originating from chromosomes 11 and 4. Contaminating sequence. Potential poly-A sequence. Contaminating sequence. Potential poly-A sequence.