S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C(5) position of cytosine 3782 (m5C3782) in 28S rRNA (PubMed:23913415, PubMed:31428936, PubMed:31722427). m5C3782 promotes protein translation without affecting ribosome biogenesis and fidelity (PubMed:31428936, PubMed:31722427). Required for corpus callosum and cerebral cortex development (By similarity). cytidine(3782) in 28S rRNA + S-adenosyl-L-methionine = 5-methylcytidine(3782) in 28S rRNA + H(+) + S-adenosyl-L-homocysteine Ubiquitous (PubMed:11978965, PubMed:12073013). Detected in placenta, heart and skeletal muscle (PubMed:11978965, PubMed:12073013). Down-regulated in some glioma; epigenetic inactivation is a hallmark of glioma patients with long-term survival. NSUN5 is located in the Williams-Beuren syndrome (WBS) critical region (PubMed:11978965, PubMed:12073013). 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 (PubMed:11978965, PubMed:12073013). Its deletion in WBS results in decreased methylation of the C(5) position of cytosine 3782 (m5C3782) in 28S rRNA (PubMed:31722427). Belongs to the class I-like SAM-binding methyltransferase superfamily. RsmB/NOP family.