DNA-Binding Proteins and Chromatin

Résumé fourni par la source

Procaryotic genomic DNA and associated proteins together form an irregularly shaped structure, designated as the nucleoid. In contrast to the range of different chromatin proteins identified in bacteria, almost all eucaryal genomes are compacted into nucleosomes, chromatin, and chromosomes by essentially the same four proteins, histones H2A, H2B, H3, and H4. This chapter describes several different families of archaeal chromatin proteins with unrelated structures, but with the common properties of abundance, small size, positive charge, and ability to bind to DNA with little or no sequence specificity. Alba does bind to both DNA and RNA in Sulfolobus species, but chromatin immunoprecipitation experiments argue convincingly that Alba is bound to genomic DNA and functions as a chromatin protein in S. solfataricus. Sul10a is the generic name of an abundant ~11 kDa DNA-binding protein investigated from S. acidocaldarius (Sac10a) and S. solfataricus (Sso10a). An NMR solution structure has been established for methanogen chromosomal protein 1 (MC1) from Methanosarcina sp. CHTI55. It is apparent that many different chromatin proteins have evolved, all of which must bind and compact DNA into complexes that are readily disassembled, or that are inherently compatible with DNA replication and transcription machineries. Gene expression requires transcription activators, for example, histone acetylases that help disassemble chromatin and so allow transcription factor access to the DNA. With the accumulation of genome sequences, it is now apparent that most archaea have the capacity to synthesize several different chromatin proteins.

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