The model shows that SIN3L and SIN3S adopt two distinct assembly modes to target different chromatin regions. The SIN3L complex has two lobes (Pst1/3 Lobe) bridged by two coiled-coil domains from Sds3/Dep1 and Rxt2/Png2, while the SIN3S complex has only one lobe (Pst2 Lobe) and two HBs (HB1 and HB2). The Pst1 Lobe in SIN3L and the Pst2 Lobe in SIN3S have similar conformations with their deacetylase active sites exposed to the space; the Pst3 Lobe in SIN3L is in a compact state with its active center buried inside and blocked. The SIN3L complex provides several domains for chromatin recognition, such as the PAH1/2 of Pst1/3 (interacting with transcription factors), the PHD of Png2 (may recognize the H3K4me3 histone marker), the PHD of Cti6 and the SWIRM domain of Laf1/2. Different combinations of these domains may be used to recognize specific promotors. The HB1 and HB2 of the SIN3S complex may offer two binding sites for the adjacent nucleosomes with H3K36me3 markers.
