HMGN proteins

Catez F, Brown DT, MisteU T, Bustin M (2002) Competition between histone HI and HMGN proteins for chromatin binding sites. EMBO Rep 3 760-766... 

The founding members of the HMGN family are HMGNl (formerly HMG-14) and HMGN2 (formerly HMG-17). Four additional HMGN proteins have been... 

Interaction of HMGN proteins with the nucleosome core particle... 

The nucleosome core particle is a relatively stable and homogenous structure that is easily prepared, and as such has formed the basis for numerous studies into chromatin structure and function. However, several recent studies have suggested that what is true for the nucleosome core may not always be true for nucleosome arrays, nor even for nucleosomes containing linker DNA. For example, the core histone tails preferentially interact with linker DNA when is it present, whereas they are constrained to bind intranucleosomal DNA in core particles [46 8]. Consequently, the activities of proteins that require access to the tails or the DNA may be affected, and it has been shown that both DNA ligase and P/CAF are less active on nucleosome core particles than other chromatin substrates [49,50]. Similar concerns apply to the interaction of HMGN proteins with nucleosome core particles, and results from studies of these complexes must be considered in the wider context of how these proteins may interact with nucleosome arrays. 

HMGN proteins are thus able to decompact chromatin and activate transcription from chromatin templates. Both activities are dependent on the C-terminal domain, and it is likely that the transcriptional enhancement is a direct result of the ability of these proteins to unfold chromatin. 

Models for chromatin unfolding by HMGN proteins 7.1. Interaction with core histone tails... 

A second model for HMGN action is that it counteracts chromatin compaction by linker histones. The ability of HMGN proteins to unfold SV40 minichromosomes and stimulate transcription from them is dependent on the presence of linker histones, and the data is consistent with HMGN counteracting the repressive... 

Association of HMGN proteins with transcription in vivo... 

HMGN proteins are small, ubiquitous, chromatin architectural elements that bind to the 147 bp nucleosome core via their highly conserved nucleosome binding domain. They bind as homodimers, interacting near base 25 of the nucleosome DNA, and near the dyad axis. When incorporated into minichromosomes, HMGN proteins decrease chromatin folding in a manner that is dependent on their C-terminal domain, with a concomitant increase in transcription. 

It has been shown that HMGN proteins stabilize the nucleosome core and prevent the dissociation of the DNA ends, observations which appear to be at odds... 

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