Cytosine methylation and the ecology of intragenomic parasites

JA Yoder, CP Walsh, TH Bestor

Research output: Contribution to journalArticlepeer-review

1563 Citations (Scopus)


Most of the 5-methylcytosine in mammalian DNA resides in transposons, which are specialized intragenomic parasites that represent at least 35% of the genome. Transposon promoters are inactive when methylated and, over time, C --> T transition mutations at methylated sites destroy many transposons. Apart from that subset of genes subject to X inactivation and genomic imprinting, no cellular gene in a non-expressing tissue has been proven to be methylated in a pattern that prevents transcription. It has become increasingly difficult to hold that reversible promoter methylation is commonly involved in developmental gene control; instead, suppression of parasitic sequence elements appears to be the primary function of cytosine methylation, with crucial secondary roles in allele-specific gene expression as seen in X inactivation and genomic imprinting.
Original languageEnglish
Pages (from-to)335-340
JournalTrends in Genetics
Issue number8
Publication statusPublished (in print/issue) - Aug 1997


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