Histone modifications act by serving as a node for the assembly of coactivators and corepressor complexes through the recognition of these modifications by proteins that contain bromodomains (recognize acetylated lysines) or chromodomains (recognize methylated lysines). This, rather than an effect on chromatin structure per se, determines effects on gene expression. Recruitment of heterochromatin protein (HP)1 through a chromodomain may also affect local DNA methylation through recruitment of DNA methyltransferases (DNMTs) and methyl binding domain (MBD) proteins. This may lead to further assembly of other histone methyl transferases (HMTs) and histone deacetylase (HDAC) complexes which enable further gene silencing to occur. Gene activation, in contrast, requires recruitment of an acrivation complex involving the TATA binding protein (TBP) and its associated factors (TAFs), chromatin remodeling complexes such as mating type switching/sucrose non-fermenting (SWI/SNF) and RNA polymerase II (RNA pol II).