Position effect takes precedence over target sequence in determination of adenine methylation patterns in the nuclear genome of a eukaryote, Tetrahymena thermophila

• Published in: Nucleic acids research Vol. 26; no. 20; pp. 4566 - 4573
• Main Authors: Karrer, Kathleen M., VanNuland, Teresa A.
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 15-10-1998
• Subjects: Adenine - analogs & derivatives; Adenine - metabolism; Animals; Blotting, Southern; Cell Line; Deoxyribonucleases, Type II Site-Specific - metabolism; DNA Methylation; DNA Replication - genetics; DNA, Protozoan - chemistry; DNA, Protozoan - genetics; DNA, Protozoan - metabolism; Escherichia coli - genetics; Escherichia coli Proteins; Plasmids - genetics; Regulatory Sequences, Nucleic Acid; Restriction Mapping; Site-Specific DNA-Methyltransferase (Adenine-Specific) - genetics; Site-Specific DNA-Methyltransferase (Adenine-Specific) - metabolism; Substrate Specificity; Tetrahymena thermophila; Tetrahymena thermophila - enzymology; Tetrahymena thermophila - genetics; Transcription, Genetic - genetics; Transformation, Genetic
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/26.20.4566

Approximately 0.8% of the adenine residues in the macronuclear DNA of the ciliated protozoan Tetrahymena thermophila are modified to N6-methyladenine. DNA methylation is site specific and the pattern of methylation is constant between clonal cell lines. In vivo, modification of adenine residues appears to occur exclusively in the sequence 5′-NAT-3′, but no consensus sequence for modified sites has been found. In this study, DNA fragments containing a site that is uniformly methylated on the 50 copies of the macronuclear chromosome were cloned into the extrachromosomal rDNA. In the novel location on the rDNA minichromosome, the site was unmethylated. The result was the same whether the sequences were introduced in a methylated or unmethylated state and regardless of the orientation of the sequence with respect to the origin of DNA replication. The data show that sequence is insufficient to account for site-specific methylation in Tetrahymena and argue that other factors determine the pattern of DNA methylation.