Post-translational modifications histone -ribosylation

As described above, histones are much more than passive structural players within chromatin. Dynamic post-translational modifications of these proteins confer specialized chemical proprieties to chromatin of both informational and structural nature with important functional implications. The highly conserved sites for acetylation, methylation, phosphorylation, ADP-ribosylation, and ubiquitination events on histone tails appear to orchestrate functional activities that range from transcriptional activation and repression to DNA repair and recombination. 

Fig. 6. Post-translational modifications of core and linker histones. The sites of acetylation, phosphorylation, poly-ADP ribosylation, methylation, and ubiquitination are incficated by numbers that correspond to the amino acid position from the N-termini of the molecules. The nomenclature of histone HI variants is as in Fig. 3. The length of C- and N-terminal tails is in relative scale between core histones to illustrate primary structural differences between these proteins.

NAD is used in post translational modification of a variety of proteins, nc>tab y 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 structure of the DNA. The other proteins are used in regulating the expression of specific genes. Poly(ADP-ribose) polymerase catalyzes the attachment of ADP-rlbose to various chromostimal pniteins. This modification, shown in Figure 9.65A, is more dramatic than a simple methylalion or phosphorj lation. The enzyme uses NAD as a substrate. Here, NAD docs 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... 

Wong M, Smulson M (1984) A relationship between nuclear poly (adenosine diphosphate ribosylation) and acetylation post-translational modifications II. Histone Studies Biochemistry 23 3726-3730... 

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