Polytene chromosome proteins chromatin

The first indication that modification of specific tail residues were linked to chromatin functional states, came from immunostaining of Drosophila polytene chromosomes with antibodies specific for H4 acetylated at defined lysines [13]. As shown in Fig. 2A, H4 acetylated at lysine 16 (H4acK16) was found almost exclusively on the transcriptional hyperactive male X chromosome (Fig. 2). (Genes on the Drosophila male X are transcribed twice as fast as their female counterparts so as to equalize levels of X-linked gene products between XY males and XX females.) In addition, H4 lysine 12 was found to remain acetylated in centric heterochromatin, while lysines 5, 8, and 16 were all under-acetylated [13]. These observations led to the suggestion that the histone N-terminal tails constitute nucleosome surface markers that can be recognized by non-histone proteins in a modification-dependent manner to alter the functional state of chromatin [13]. 

DeCamiUis M., Cheng N.S., Pierre D., and Brock H.W. 1992. The polyhomeotic gene of Drosophila encodes a chromatin protein that shares polytene chromosome-binding sites with Polycomb. Genes Dev. 6 223-232. 

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