Histone lysine methylation is an important chromatin modification that can be catalyzed to a
mono-, di-, or tri-methyl state. An ongoing challenge is to decipher how these different
methyllysine histone marks can mediate distinct aspects of chromatin function. The fission
yeast checkpoint protein Crb2 is rapidly targeted to sites of DNA damage after genomic
insult, and this recruitment requires methylation of histone H4 lysine 20 (H4K20). Here we
show that the tandem tudor domains of Crb2 preferentially bind the di-methylated H4K20 …