The impact of 55−́CG‐3′ methylation on the activity of different eukaryotic promoters: A comparative study

Abstract

The inhibiting or inactivating effects of position-specific promoter methylation in different viral or human cellular promoters Ad2 E2AL, SV40, LTR-MMTV, HSV-tk, TNFα) have been compared by in vitro 5′-CCGG-3′ methylation by M-HpaII or the M-SssI DNA-methyltransferase, respectively. In most promoters, 5′-CG-3′ methylation reduces activity to a few percent of that of mock-methylated controls. The number of 5′-CG-3′ dinucleotides in a promoter does not strictly correlate with the extent of methylation inhibition. The LTR-MMTV promoter, which lacks 5′-CG-3′ dinucleotides, is not affected by methylation. The late E2A promoter of Ad2 DNA cannot be inactivated by 5′-CCGG-3′ methylation when the construct carries the strong cytomegalovirus enhancer devoid of this sequence. In contrast, 5′-CG-3′ methylation shuts this promoter off even in the presence of this enhancer.