Enables polypeptide N-acetylgalactosaminyltransferase activity. Acts upstream of or within protein O-linked glycosylation. Predicted to be located in membrane. Predicted to be integral component of membrane. Predicted to be active in Golgi apparatus. Is expressed in heart; liver; lung; metanephros; and nervous system. Orthologous to human GALNT13 (polypeptide N-acetylgalactosaminyltransferase 13). [provided by Alliance of Genome Resources, Apr 2022]