Nucleic acid, methyl fragments

Methylases specific for each of the four bases of sRNA (97) and for adenine and cytosine of DNA (98) are available. Selective modification of a nucleic acid or its oligonucleotide fragments before digestion with a specific nuclease gives additional dimensions for selective degradation. Use of C-methyl labelled S-adenosylmethionine permits selective isotopic labelling by these enzymes. 

The sugar components ofDNA- and RNA-based nucleic acids participate in the formation of nucleoside subunits and under pyrolytic conditions will lead to a specific 2-methylfuran (la) residue. RNA-based nucleic acids will also exhibit fragment ions due to 2-methyl-4-hydroxyfuran (lb) (Fig. 3). This behavior is typical of ribose derivatives. However, the attachment of the fragments la or lb to other ions formed in the fragmentation processes is unusual. The la unit, for example, undergoes dimerization, and ions con-... 

Kuijpers W, Huskens J, Koole L, van Boeckel C. Synthesis of a well defined phosphate methylated DNA fragment The application of potassium carbonate in methanol as deprotecting agent. Nucleic Acids Res 18 5197-5201, 1990. 

In the dimethylsulfate (DMS) technique, the end-labeled DNA segment is treated with DMS, cleaved chemically at its methylated G residues, and the resulting fragments separated electrophoretically this entire procedure is described in detail in the entry Nucleic acid sequencing (see). As in the previous technique, gaps or footprints in the autoradiogram identify the position and nature of the DNA sequences that bind the protein in question. 

---