We analyze the histograms for the lengths of the 16 possible distinct repeats of identical dimers, known as dimeric tandem repeats, in dna sequences. For coding regions, the probability of finding a repetitive sequenc...
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We analyze the histograms for the lengths of the 16 possible distinct repeats of identical dimers, known as dimeric tandem repeats, in dna sequences. For coding regions, the probability of finding a repetitive sequence of ℓ copies of a particular dimer decreases exponentially as ℓ increases. For the noncoding regions, the distribution functions for most of the 16 dimers have long tails and can be approximated by power-law functions, while for coding dna, they can be well fit by a first-order Markov process. We propose a model, based on known biophysical processes, which leads to the observed probability distribution functions for noncoding dna. We argue that this difference in the shape of the distribution functions between coding and noncoding dna arises from the fact that noncoding dna is more tolerant to evolutionary mutational alterations than coding dna.
The pattern of histone H4 acetylation in different genomic regions has been investigated by immunoprecipitating oligonucleosomes from a human lymphoblastoid cell line with antibodies to H4 acetylated at lysines 5, 8, ...
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The pattern of histone H4 acetylation in different genomic regions has been investigated by immunoprecipitating oligonucleosomes from a human lymphoblastoid cell line with antibodies to H4 acetylated at lysines 5, 8, 12 or 16. dna from antibody-bound or unbound chromatin was assayed by slot blotting. Pol I and pol II transcribed genes located in euchromatin were shown to have levers of H4 acetylation at lysines 5, 8 and 12 equivalent to those in input chromatin, but to be slightly enriched in H4 acetylated at lysine 16. In no case did the acetylation level correlate with actual or potential transcriptional activity. All acetylated histone H4 isoforms were depleted in non-coding, simple;repeat dna in heterochromatin, though the extent of depletion varied with the type of heterochromatin and with the isoform, Two single copy genes that map within or adjacent to blocks of paracentric heterochromatin are depleted in H4 acetylated at lysines 5, 8 and 12, but not 16, Consensus sequences of repetitive elements of the Alu family (SINES, enriched in R bands) were associated with H4 that was more highly acetylated at all four lysines than input chromatin, while H4 associated with KpnI elements (LINES, enriched in G bands) was significantly underacetylated.
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