In E. coli, a methyltransferase enzyme encoded by the dam gene recognizes the sequence 5' GATC-3' and

Question:

In E. coli, a methyltransferase enzyme encoded by the dam gene recognizes the sequence 5' GATC-3' and attaches a methyl group to the N6 position of adenine. E. coli strains that have the dam gene deleted are known to have a higher spontaneous mutation rate than normal strains. Explain why.