Histonlignende

Histonlignende, or histone-like, refers to a group of DNA-binding proteins that resemble histones in their functions or structural motifs, and that play a key role in genome organization and regulation in prokaryotes and archaea. Although they are distinct from eukaryotic histones, histone-like proteins can compact DNA, influence topology, and modulate transcription and replication.

In bacteria, common histone-like proteins include HU, IHF, H-NS, Fis, and Dps. HU and IHF are small dimeric proteins that bend DNA and assist in nucleoid organization and recombination. H-NS acts as a global transcriptional silencer and helps shape the nucleoid in response to environmental changes. Fis is involved in transcriptional regulation and DNA topology, while Dps forms protective, compacted complexes with DNA during stress conditions.

In archaea, histone-like proteins range from archaeal histones HMfA/HMfB, which can assemble into nucleo-like structures that wrap DNA, to Alba family proteins that bind DNA and RNA and cooperate with histones to modulate chromatin organization. Additional small DNA-binding proteins, such as Cren7 in some crenarchaeota, contribute to chromatin structure and gene regulation.

Structure and mechanism of histone-like proteins are diverse. Many are small and highly basic, forming dimers or oligomers that interact with DNA through electrostatic and sequence-nonspecific contacts. They can bend, bridge, or wrap DNA, influencing supercoiling and accessibility to transcription machinery.

Evolutionarily, histone-like proteins are widespread and are thought to represent ancient strategies for organizing genomes, predating eukaryotic histones in function if not in form. They remain essential for chromosome maintenance, stress responses, and gene regulation in their respective domains.