Functions as transcription repressor, probably via its interaction with histone deacetylase complexes (PubMed:16820529, PubMed:18070604). Involved in the functional recruitment of the class 1 Sin3-histone deacetylase complex (HDAC) to the nucleolus (PubMed:16820529). Binds DNA, apparently without sequence-specificity, and bends bound double-stranded DNA (PubMed:19015240). Binds phosphoinositol phosphates (phosphoinositol 3-phosphate, phosphoinositol 4-phosphate and phosphoinositol 5-phosphate) via the same basic sequence motif that mediates DNA binding and nuclear import (PubMed:19015240, PubMed:26609676). Functions as transcription repressor; isoform 2 has lower transcription repressor activity than isoform 1 and isoform 3. Functions as transcription repressor; its activity is marginally lower than that of isoform 1. Interacts with components of the histone deacetylase complex SIN3A, HDAC1 and HDAC2 (PubMed:16820529). Binds histones and nucleosomes (PubMed:19015240). Interacts with FEZ1 (PubMed:16484223). Detected in brain and ovary, and at lower levels in heart, small intestine, lung, kidney, skeletal muscle, stomach and spleen (at protein level) (PubMed:18070604). Ubiquitous; expressed in all tissues tested with highest levels in testis (PubMed:14680513). Up-regulated by TGFB1. The zinc-finger domain mediates direct interaction with DNA and phosphoinositol phosphates (phosphoinositol 3-phosphate, phosphoinositol 4-phosphate and phosphoinositol 5-phosphate) (PubMed:26609676). In vitro oxydation causes reversible disulfide bond formation between Cys residues in the zinc-finger domain and reversible loss of zinc ion binding (PubMed:26609676). Belongs to the SAP30 family.