What should we expect of a histone code

It is now a decade since evidence was first presented that the modification (acetylation) of particular residues on the histone tails was functionally significant [13,14]. Since then, it has been established beyond all reasonable doubt that specific modifications and combinations thereof, mediate protein-protein interactions crucial for the long-term and short-term regulation of transcriptional activity. Some of these interactions involve the modifying enzymes themselves, and recent data shows how particular histone tail modifications can interact, both to put in place defined patterns of modification and to control their recognition. Examples are presented in Table 1. But do these findings support the existence of a histone code  

Examples of residue-specific histone modifications associated with defined functional 

Modification Organism Modific n set by Modific n read by Chromatin state Refs. 

H4acK16 Drosophila MOF ISWI binding decreased Decondensation of male X, transcription up-regulated 13,83-86 

H3meK9 Drosophila, mammals Su(var)3-9, SUV39H HPl binding Heterochromatin formation 33-36,40 

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