A rapid synthesis of histone mRNAs is required during cell division in order to produce large amounts of histone proteins. Critical to this process are the replication-dependent histone genes that are upregulated during the G1/S phase of cell cycle (29). A specific RefSeq project was undertaken with the aim of curating the full set of replication-dependent histone protein coding genes in human and mouse. These genes have a canonical 3′ histone downstream element (HDE) sequence in the genomic sequence and the resultant mature mRNAs characteristically lack poly(A) tails and instead terminate shortly after an RNA stem-loop structure (30). The HDE element is found on the precursor transcript but is not included on the processed transcript represented by RefSeq. The location of the conserved 16 nucleotide stem-loop structure sequence is indicated on the RefSeq record as a feature annotation entitled ‘stem-loop’. An example can be seen on the RefSeq entry NM_003539.3 for HIST1H4D (GeneID: 8360). To date, 127 human and mouse replication-dependent histone RefSeq records have been curated and a RefSeq attribute added which can be used to retrieve these records from the Nucleotide database using the search string ‘replication-dependent histone[properties]’.
