DNA methylation and gene activity

PERSPECTIVES AND SUMMARY 93 BIOCHEMISTRY OF DNA METHYLATION . . ...... ....... . . . 95 Occurrence of Modified Bases ...... .... . . . . . . ......... . . . ... .. 95 Maintenance and de novo Methylations ........ .. ... ........ ..... ..... .. ... 96 Methods to Determine Methylated Bases .. ........ .. . . . . . . . .. . . ...... . ...... ..... . .... . . . 99 Distribution of 5-Methylcytosine ... .. ... . .. .. . ....... .... . ..... .. ... .. . ... . .... ......... .... . 100 DN A Methylatiun and Structural Changes uf DN A 102 THE BIOLOGICAL FUNCTION OF DNA METHYLATION . . . . . . 103 DNA Methylation--a Regulatory Signal in Eukaryotic Gene Expression . ... . . . .. . 103 Correlations ... . ..... .. .. . . . . . . .... . .. .... . . . . . . . . . . . . ......... ......... . ......... . ...... . ...... 105 The Drosophila Problem . . .. .. ..... ..... .. .. .... . ... .... .... . . . .... ... .. . . ... .... ... .. .... . 109 Treatment of Cells with 5-Azacytidine Can Lead to the Activation of Previously Dormant Genes ..... ..... ... .. .... .. . . .... .. ..... ....... ..... . . .. ... ..... . . . .. .. . . 110 DNA Methylation at Specific Sites is Causally Related /0 Gene Inactivation ..... . . 112 Additional Observations . . .. .. . .. . . . .. .. ... . . .. . ......... . .... .... . ........ . . . . .... .... . .. . . 115 Overall Conclusions ..... 116 DNA Methylation and Genetic Recombination . .... ... . . .. .. . . .... ... .. ..... . . ..... .. .... 117 A Model of Herpes Simplex Virus Latency 117 IN SEARCH OF MORE COMPLEX GENETIC CODING SIGNALS . ......... . .. 118 OUTLOOK ........ 118