S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the N(7) position of a guanine in 18S rRNA (PubMed:25851604). Requires the methyltransferase adapter protein TRM112 for full rRNA methyltransferase activity (PubMed:25851604). Involved in the pre-rRNA processing steps leading to small-subunit rRNA production independently of its RNA-modifying catalytic activity (PubMed:25851604). Important for biogenesis end export of the 40S ribosomal subunit independent on its methyltransferase activity (PubMed:24086612). Locus-specific steroid receptor coactivator. Potentiates transactivation by glucocorticoid (NR3C1), mineralocorticoid (NR3C2), androgen (AR) and progesterone (PGR) receptors (PubMed:24488492). Required for the maintenance of open chromatin at the TSC22D3/GILZ locus to facilitate NR3C1 loading on the response elements (PubMed:24488492). Required for maintenance of dimethylation on histone H3 'Lys-79' (H3K79me2), although direct histone methyltransferase activity is not observed in vitro (PubMed:24488492). a guanosine in 18S rRNA + S-adenosyl-L-methionine = an N(7)-methylguanosine in 18S rRNA + S-adenosyl-L-homocysteine Heterodimer with TRMT112; this heterodimerization is necessary for the metabolic stability and activity of the catalytic subunit BUD23 (PubMed:25851604, PubMed:34948388). Interacts with GRIP1 (PubMed:24488492). Localized diffusely throughout the nucleus and the cytoplasm (PubMed:24488492). Localizes to a polarized perinuclear structure, overlapping partially with the Golgi and lysosomes (PubMed:25851604). Localization is not affected by glucocorticoid treatment (PubMed:24488492). Widely expressed, with high levels in heart, skeletal muscle and kidney. Detected at high levels in bronchial brushings and in normal lung (at protein level). In fetal lung tissue, expressed in the developing bronchial lumen lining cells (at protein level). Tends to be down-regulated in lungs affected by inflammatory diseases or neoplasia (at protein level). Expressed in immune cells, including B and T lymphocytes and macrophages. Up-regulated in CD8+ T lymphocytes by treatment with anti-CD3 and in B lymphocytes by treatment with CD40 ligand and anti-B cell receptor antibody. In macrophages, no induction following LPS treatment. Down-regulated by a combined treatment with TNF and IFNG (at protein level). May be ubiquitinated and targeted to degradation in response to pro-inflammatory cytokine signaling. BUD23 is located in the Williams-Beuren syndrome (WBS) critical region. WBS results from a hemizygous deletion of several genes on chromosome 7q11.23, thought to arise as a consequence of unequal crossing over between highly homologous low-copy repeat sequences flanking the deleted region. Haploinsufficiency of BUD23 may be the cause of certain cardiovascular and musculo-skeletal abnormalities observed in the disease. Belongs to the class I-like SAM-binding methyltransferase superfamily. BUD23/WBSCR22 family.