Figure 3.

BcgI methylation of oligoduplexes. (a) Reactions, at 37°C in buffer M (which includes ³H-SAM), contained 60 nM BcgI protein and one of the following oligoduplexes at 300 nM, as indicated on the right: (18 bp specific duplex, bottom strand methylated), white squares; (42 bp, bottom strand methylated), white circles; (top strand methylated), black circles; (both strands methylated), white triangles; 42S (neither strand methylated), white inverted triangles; 42NS (42 bp non-specific duplex, no recognition site), black squares. Samples were withdrawn from the reaction at the times indicated, quenched and the amount of radiolabel in the DNA at each time point was then measured as in the ‘Materials and Methods’ section. (b) Data from the reactions on 42S, 42NS and are plotted on an extended time scale (400 instead of 60 min) and a reduced dpm scale (2000 instead of 10 000 dpm). Each data point is the mean of three repeats; error bars denote standard deviations. The lines drawn through the data in (a) from , and correspond to the best fits to exponential functions. The lines drawn through the data from 42 S, 42NS and , in both (a) and (b), are fits to linear slopes.