UniProt Summary: O-acetyltransferase that catalyzes 9-O-acetylation of sialic acids (PubMed:20947662, PubMed:26169044). Sialic acids are sugars at the reducing end of glycoproteins and glycolipids, and are involved in various processes such as cell-cell interactions, host-pathogen recognition (PubMed:20947662, PubMed:26169044). {ECO:0000269|PubMed:26169044, ECO:0000305|PubMed:20947662}.