The human H1 histone gene FNC16 is functionally expressed in proliferating HeLa S3 cells and is down-regulated during terminal differentiation in HL60 cells

The human H1 histone gene FNC16 resides in a 2.7-kb EcoRI fragment present in a histone gene cluster that also contains one copy of each of the core (H2A, H2B, H3, and H4) histone genes. The cap site for FNC16 H1 mRNA is located 58 nucleotides upstream of the ATG translational start codon, and S1 nuclease protection analysis clearly distinguishes between correctly initiated FNC16 transcripts and transcripts from other nonidentical H1 histone genes. We have observed, using S1 analysis, that the FNC16 H1 histone gene is expressed in a replication-dependent manner in HeLa cells and is expressed in proliferating, but down-regulated in differentiated, HL60 cells. Similar results were found in HeLa S3 and HL60 cells for the cell cycle-dependent human H4 histone gene FO108. Nuclear extracts derived from HeLa S3 cells are capable of directing FNC16 H1 histone gene transcription in vitro. This finding is consistent with previous work that established at least two sites for protein-DNA interaction in vitro in the proximal promoter region of this gene. We habe observed a difference in the extent to which the FNC16 H1 histone gene is expressed in HeLa S3 and proliferating HL60 cells, which suggests that this H1 gene is differentially regulated in various cell types. Although results reported for a potentially identical human H1 histone gene designated Hh8C (La Bella, F., Zhong, R., and Heintz, N. (1988) J. Biol. Chem. 263, 2115-2118) support differential regulation of human H1 genes in various cell types, their observations that the Hh8C gene is not expressed in HeLa cells and that the restriction patterns differ indicate that FNC16 and Hh8C are different H1 genes.