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PubMed

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Comparative analysis of DNA methylation in tobacco heterochromatic sequences

Chromosome research. 2000 ; 8 (6) : 527-41.

Chromosome Res
ISSN 0967-3849
Source

Language English Country Netherlands Media print

Document type Comparative Study, Journal Article, Research Support, Non-U.S. Gov't

Persistent link https://www.medvik.cz/link/pmid11032322

PubMed 11032322
DOI 10.1023/a:1009223823327
Knihovny.cz E-resources

MeSH
Adenine analogs & derivatives pharmacology MeSH
Cytosine metabolism MeSH
DNA, Plant drug effects isolation & purification metabolism MeSH
Transcription, Genetic MeSH
Genome, Plant MeSH
Heterochromatin metabolism MeSH
Interphase MeSH
Plants, Toxic * MeSH
Cells, Cultured MeSH
DNA Methylation * MeSH
Nucleotides metabolism MeSH
Repetitive Sequences, Nucleic Acid MeSH
DNA Restriction Enzymes MeSH
DNA, Satellite MeSH
Blotting, Southern MeSH
Nicotiana genetics MeSH
Publication type
Journal Article MeSH
Research Support, Non-U.S. Gov't MeSH
Comparative Study MeSH
Names of Substances
9-(2,3-dihydroxypropyl)adenine MeSH Browser
Adenine MeSH
Cytosine MeSH
DNA, Plant MeSH
Heterochromatin MeSH
Nucleotides MeSH
DNA Restriction Enzymes MeSH
DNA, Satellite MeSH

Cytosine methylation levels and susceptibility to drug-induced hypomethylation have been studied in several Nicotiana tabacum (tobacco) DNA repetitive sequences. It has been shown using HapII, MspI, BamHI and Sau3AI methylation-sensitive restriction enzymes that the degree of 5'-mCmCG-3' methylation varied significantly between different repeats. There were almost saturation levels of 5-methylcytosine at the inner (3') cytosine position and variable degrees of methylation at the outer (5') cytosine at the enzyme recognition sites. The non-transcribed high copy satellite sequences (HRS60, GRS) displayed significant heterogeneity in methylation of their basic units while middle repetitive sequences (R8.1, GRD5, 5S rDNA) were more uniformly modified at both cytosine residues. Dihydroxypropyladenine (DHPA) treatment, which is thought to reduce DNA methyltransferase activity by increasing S-adenosylhomocysteine levels, resulted in extensive demethylation of the outer cytosine in all repeats, and the partial hypomethylation of cytosines at the inner positions in less densely methylated repeats such as HRS60 and GRS. The results suggest that hypomethylation of 5'-mCmCG-3' sites with DHPA is a gradual non-random process proceeding in the direction mCmCG-->CmCG-->CCG. The 18S-5.8S-25S rDNA was remarkably hypomethylated relative to the 5S rDNA at all restriction sites studied. Fluorescence in-situ hybridization showed that DNA decondensation within and between the 18S-5.8S-25S and 5S rDNA loci was variable in different nuclei. All nuclei had condensed and decondensed sequence. The chromatin of 18S-5.8S-25S rDNA was more readily digested with micrococcal nuclease than the 5S rDNA suggesting that the overall levels of decondensation were higher for 18S-5.8S-25S rDNA. Variable decondensation patterns within and between loci were also observed for GRS and HRS60. Cytosine methylation of the tobacco repeats is discussed with respect to transcription, overall levels of condensation and overall structure.

Institute of Biophysics Academy of Sciences of the Czech Republic Brno

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