Variant histone H3 which replaces conventional H3 in a wide range of nucleosomes in active genes. Constitutes the predominant form of histone H3 in non-dividing cells and is incorporated into chromatin independently of DNA synthesis. Deposited at sites of nucleosomal displacement throughout transcribed genes; suggesting that it represents an epigenetic imprint of transcriptionally active chromatin. Nucleosomes wrap and compact DNA into chromatin; limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation; DNA repair; DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones; also called histone code; and nucleosome remodeling. {ECO:0000269|PubMed:14718166; ECO:0000269|PubMed:15776021; ECO:0000269|PubMed:16258499}.