Polytene chromosome proteins

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]. 

Like the puffs of polytene chromosomes (Chapter 28), which may have a similar structure, lampbrush chromosomes appear to be actively engaged in transcription. Approximately 3% of the DNA may be functional in producing mRNA that is accumulated within the oocyte and is used as a template for protein synthesis during early embryonic development.90... 

Stress proteins. Ritossa reported in 1962 that when Drosophila were suddenly warmed from 25°C to 36-37°C, a series of new puffs could be observed within the polytene chromosomes of the salivary glands.442 These same puffs, which were also seen after other stresses, appeared within a few minutes and were associated with formation of new mRNAs. This heat-shock phenomenon was subsequently found to be universal. It is observed in all species of animals as well as in plants and bacteria.443 48... 

The gene for Drm-SP-1 has been localized by in situ hybridization to polytene chromosomes at 70A (20). This 266 bp single-copy gene with one intron has been cloned and expressed when linked to the heat shock promoter or the yolk protein 1 promoter (E. Kubli and coworkers as cited by (41)). Other aspects of Drm-SP-1 molecular biology are summarized by Chen (41). 

The DNA sequences which code for proteins are located mainly in the interband regions of the polytene chromosome. According to Crick s calculations, the mean amount of DNA in the interband region in the Drosophila genome is enough to code for a protein with a molecular weight of 30,000-40,000. 

A very clear picture of asynchrony and local heterogeneity of DNA synthesis in the chromosomes was obtained in studies of DNA synthesis in the polytene chromosomes of insect salivary glands. We shall describe the characteristics of synthesis of DNA, RNA, and proteins in these chromosomes in greater detail later in connection with our examination of chromosomal puffs. At this point, however, I shall mention the results of experiments (Plaut, 1963 Plaut and Nash, 1964) in which asynchrony of DNA synthesis in different parts of individual chromosomes was demonstrated very clearly. 

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. 

Mapping Protein Distributions on Polytene Chromosomes by Immunostaining ... 

Zink B., Engstrom Y., Gehring W.J., and Paro R. 1991. Direct interaction of the Polycomb protein with Antennapedia regulatory sequences in polytene chromosomes of Drosophila melanogaster. EMBO J. 10 153-162. 

Acid fast green staining of proteins of polytene chromosomes Protocol 24... 

Staining polytene chromosomes with antibodies to proteins Protocol 31... 

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