CDK4 is thought to disrupt the interaction between Rb and one of these proteins.
Overexpression of one member of this family of proteins represses the accumulation of extrachromosomal rDNA circles in budding yeast. The first known examples of this class of proteins  were identified using resin-conjugated trapoxin. Phosphorylation of Rb by cyclin D/CDK4 is thought to disrupt the interaction between Rb and one of these proteins. These proteins eliminate bromodomain-binding regions, and they can be inhibited by trichostatin A. A highly conserved subset of these proteins is activated by NAD+ and is named for one of its yeast members, Sir2. The action of these proteins upon N-terminal lysines always results in compaction of chromatin and reduction of transcription. Their action is opposed by proteins called HATs. For 10 points, name this class of enzymes that removes a certain post-translational modification from histones.
Overexpression of one member of this family of proteins represses the accumulation of extrachromosomal rDNA circles in budding yeast.
histone deacetylases [or HDACs; or lysine deacetylases; or LDACs; prompt on deacetylases until "histones" is read, accept deacetylases after "histones" is read; accept sirtuins until the end of the second sentence; prompt on sirtuins afterwards; do not accept histone acetyltransferases or HATs, do not accept histones or histone methlytransferases]