Histone chaperone that stabilizes pre-existing histone tetramers and regulates replication-independent histone exchange on chromatin. Required for normal chromatin refolding in the coding region of transcribed genes, and for the suppression of spurious transcription. Binds DNA and histones and promotes nucleosome assembly (in vitro). Facilitates formation of tetrameric histone complexes containing histone H3 and H4 (By similarity). Modulates RNA polymerase 1-mediated transcription (By similarity). Binds DNA, with a preference for branched DNA species, such as Y-form DNA and Holliday junction DNA (By similarity). Interacts with histones. Interacts with a heterotetrameric complex formed by histone H3 and H4, especially when the histone tetramer is not bound to DNA. The acidic C-terminal domain mediates interaction with histone H3/H4 complexes. Belongs to the SPT2 family. Contaminating sequence. Potential poly-A sequence.