Gene Nonhistone chromosomal protein

Transcription is the first and often most critically regulated step in gene expression. In eukaryotes, multisubunit RNA polymerases transcribe genes, whose DNA is packaged together with histones and other nonhistone chromosomal proteins into chromatin, which is notoriously intractable and not easily transcribed by those polymerases in vitro. A central question driving research on eukaryotic transcription has therefore been, How is timely and efficient transcription of chromatin-embedded genes achieved in eukaryotic cells ... 

Whether a gene is positioned in active or inactive chromatin certainly also plays a large role in whether or not transcription can occur. The various elements which define active chromatin (sensitivity and hypersensitivity to nucleases, presence of HMG proteins, modifications of both histone and nonhistone chromosomal proteins, DNA methylation) have recently been reviewed (Weisbrod, 1982 Razin and Riggs, 1980). With a few exceptions, there is no clear idea how the DNA sequences and proteins which are known to modulate transcription relate to the formation of active chromatin. Such a discussion must therefore be deferred to a later date. 

NAD is used in posttranslational modification of a variety of proteins, notably some of the proteins of the chromosomes. The chromosomes are composed of DNA, histones, and nonhistone proteins. The histones, which are distinguished by their high content of basic amino acids, serve as a scaffold and maintain the coiled and folded structiue of the DNA. The other proteins are used in regulating the expression of specific genes. Poly(ADP-ribose) polymerase catalyzes the attachment of ADP-ribose to various chromosomal proteins. This modification, shown in Figure 9.65A, is more dramatic than a simple methylation or phosphorylation. The enzyme uses NAD as a substrate. Here, NAD does not serve its usual role as an oxidant or reductant. The ADP-ribosyl moiety of NAD is donated to the acceptor protein. A molecule of nicotinamide is discharged with each event of... 

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