sentence: Among the ubiquitin-specifc proteases characterized , Ubp10 / Dot4 is remarkable ; this is a deubiquitylating enzyme related to gene-silencing that regulates histone ubH2B deubiquitylation and helps to localise the histone deacetylase Sir2 complex at telomeres , cryptic mating type loci ( HML and HMR ) and rDNA loci [ 24 ] , [ 25 ] .