S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the N(7) position of a guanine in 18S rRNA. Requires the methyltransferase adapter protein TRM112 for full rRNA methyltransferase activity. Involved in the pre-rRNA processing steps leading to small-subunit rRNA production independently of its RNA-modifying catalytic activity. Important for biogenesis end export of the 40S ribosomal subunit independent on its methyltransferase activity. Locus-specific steroid receptor coactivator. Potentiates transactivation by glucocorticoid (NR3C1), mineralocorticoid (NR3C2), androgen (AR) and progesterone (PGR) receptors. Required for the maintenance of open chromatin at the TSC22D3/GILZ locus to facilitate NR3C1 loading on the response elements. Required for maintenance of dimethylation on histone H3 'Lys-79' (H3K79me2), although direct histone methyltransferase activity is not observed in vitro. 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. Interacts with GRIP1. Localized diffusely throughout the nucleus and the cytoplasm. Localizes to a polarized perinuclear structure, overlapping partially with the Golgi and lysosomes. Localization is not affected by glucocorticoid treatment. May be ubiquitinated and targeted to degradation in response to pro-inflammatory cytokine signaling. Belongs to the class I-like SAM-binding methyltransferase superfamily. BUD23/WBSCR22 family.