The correlation between DNA methylation and chromatin structure, as it relates to transcriptional activity, is demonstrated by the observation that there are several proteins, that bind to methylated CpGs but not to unmethylated CpGs, whose functions are integrated into transcriptional regulation. There are currently 15 genes in the human genome that encode proteins that bind to methyl-CpG in DNA. These 15 proteins are divided into 3 subfamilies identified by structural similarities. These sub-families are the methyl binding domain (MBD) proteins, the methyl-CpG-binding zinc finger proteins (also called the Kaiso family), and the SRA domain ( S ET and R ING finger domain A ssociated) containing proteins. The SET domain is so-called because it was first identified in three Drosophila proteins called S uppressor of variegation variant 3-9 [Su(var)3-9], E nhancer of zeste, and T rithorax. The RING domain is a zinc-finger-like domain which gets its name from the term R eally I nteresting N ew G ene.
Modern journaling file systems are designed such that tools such as fsck do not need to be run after unclean shutdown (. crash). The UFS2 Filesystem in FreeBSD has a background fsck, so it is usually not necessary to wait for fsck to finish before accessing the disk. Full copy-on-write file systems such as ZFS and Btrfs are designed to avoid most causes of corruption and have no traditional "fsck" repair tool. Both have a "scrub" utility which examines and repairs any problems; in the background and on a mounted filesystem.