Rapid detection of functional expression of C-5-DNA methyltransferases in yeast.

We have previously employed the cytosine-5-DNA methyltransferase (MTase), M. Sss I, as a probe for chromatin architecture in intact cells. Although M. Sss I offers the highest resolution of any currently available MTase, the difficulty in establishing stable, methylation-positive strains poses a barrier to its general utility as a chromatin probe. We describe a simple screen for M. Sss I-expressing strains that eliminates the purification of PCR products amplified from bisulfite-treated DNA, use of radioisotopes, polyacrylamide sequencing gel electrophoresis, and autoradiography. The high throughput of the method now makes it feasible to introduce M. Sss I into a variety of wild-type and mutant genetic backgrounds.