Putative methyltransferase NSUN5 is an enzyme that in humans is encoded by the NSUN5 gene. S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the C5 position of cytosine 3782 (m5C3782) in 28S rRNA. m5C3782 promotes protein translation without affecting ribosome biogenesis and fidelity. Required for corpus callosum and cerebral cortex development (By similarity). This gene is deleted in Williams syndrome, a multisystem developmental disorder caused by the deletion of contiguous genes at 7q11.23. Alternative splicing of this gene results in two transcript variants encoding different isoforms.