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Title: Homopolymer-rich regions in mammalian DNA
Author: Shenkin, Alan
ISNI:       0000 0001 3402 8851
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1974
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The presence of deoxyadenylate-rich (dA-rich) and deoxyguanylate-rich (dG-rich) regions in mammalian DNA has been demonstrated by hybridisation with [5H] poly(U) and [5H] poly(C). For BHK-21/CI3 cells, the maximum levels of these homopolymer-rich regions, as detected by the hybridisation technique, are about 0.41% of the DNA for dA-rich, and 0.1% of the DNA for dG-rich regions. Since the hybrids are largely sensitive to digestion with RNase, it is probable that the majority of hybrid molecules contain mismatched base-pairs. 0.13% of the DNA consists of dA-rich regions ranging in size from 25-130 nucleotides long and containing about 2-6% of bases other than adenine. On the other hand, dG-rich regions less than 40 nucleotides long comprise 0.07% of the DNA and contain 10-30% of bases other than guanine. Exhaustive RNase digestion of the hybrids enables detection of pure deoxyhomopolymeric regions in the DNA. Pure sequences of poly(dA) of average size about 31 nucleotides long account for 0.008% of BHK-21/C13 DNA, whereas poly(dG) sequences about 17 nucleotides long comprise 0.0016% of the-DNA. The organisation of these sequences within the genome has been investigated. Both dA-rich and dG-rich regions are present within DNA sequences of widely varying base composition. Extensive shearing of the DNA is required to produce some enrichment for dA-rich sequences in the A + T rich fraction, although dG-rich sequences are slightly enriched in the (3- + C rich fraction of even unsheared DNA. The buoyant density of hybrid molecules was found to be significantly greater than that of the unhybridised DNA only when highly sheared. DNA was used. Furthermore, dA- rich and dG-rich regions were shown to be associated with rapidly, intermediately, and slowly renaturing DNA sequences. These findings all suggest that the dA-rich and dA-rich regions have a widespread distribution throughout DNA molecules. The pure poly(dA) and poly(dG) sequences also appear to be scattered throughout DNA molecules. In situ hybridisation studies with C5H] poly(U) further suggest that the dA~rich regions are not localised to any particular chromosome or to any specific region of the chromosomes. Analysis of DNA from a number of different species has shown that, in general, the dA-rich and dG-rich regions are present to a much higher level in mammalian DNA than in bacterial, bacteriophage, and mammalian viral DNAs. Evidence for the existence of A-rich, U-rich and G-rich RNA species in BHK-21/015 cells has also been obtained. The characteristics of the homopolymer-rich regions in DNA suggest that the dA-rich and pure poly(dA) sequences are more likely to have a significant role than dG-rich and poly(dG) sequences. The possible functions of these unusual deoxynucleotide sequences are reviewed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available