Lysine residues TOPICAL

The topic of histone acetylation has been the subject of extensive reviews (Dixon et al., 1975 Dixon, 1976 Allfrey, 1977 Isenberg, 1979). Acetylation occurs at specific lysine residues. In the case of the four core histones the acetylation sites are all located in the amino-terminal half of the molecule. 

The numerous negative charges are significant in several respects (1) they contribute to the poor membrane penetrability—heparin is ineffective when applied by the oral route or topically onto the skin and must be injected (2) attraction to positively charged lysine residues is involved in complex formation with ATIII (3) they permit binding of heparin to its antidote, protamine (polycationic protein from salmon sperm). 

Numerous studies performed with E. coli have established that, in E. coli, biotin regulates very efficiently its biosynthetic pathway, with an absolute specificity, the biotin vitamers being inactive. As the topics has been largely reviewed, it will be only summarized here. The regulation occurs at the transcriptional level and the biotin operon repressor (BirA) has been well characterized. This 33.5 kDa bifiinctional protein is both an enzyme and a transcriptional regulator (Figure 21). It activates biotin into biotinyl-5 -AMP with ATP (reaction a) and transfers biotin on a specific lysine residue of the biotin accepting proteins (in E. coli, the biotin carboxyl carrier protein (BCCP), a subunit of acetyl-CoA carboxylase) (reaction b). When all the... 

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