Enables polypeptide N-acetylgalactosaminyltransferase activity. Predicted to be involved in protein O-linked glycosylation via serine and protein O-linked glycosylation via threonine. Predicted to be located in perinuclear region of cytoplasm. Predicted to be active in Golgi apparatus. Orthologous to human GALNT1 (polypeptide N-acetylgalactosaminyltransferase 1). [provided by Alliance of Genome Resources, Apr 2022]