Macronuclear replacement variant which replaces conventional H3 in a subset of nucleosomes. 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. Functions redundantly to H3.3. H3.4 deposition is mainly transcription-associated, DNA replication-independent. Although not essential for vegetative growth, minor H3 variants are required for producing viable conjugation progeny by affecting late developmental stages of conjugation. The nucleosome is a histone octamer containing two molecules each of H2A, H2B, H3 and H4 assembled in one H3-H4 heterotetramer and two H2A-H2B heterodimers. The octamer wraps approximately 147 bp of DNA. Localizes mainly to the large, transcriptionally active, somatic macronucleus (MAC) and only faintly to the small, transcriptionally inert, germ line micronucleus (MIC). Up-regulated in the absence of H3.3. Belongs to the histone H3 family.