Recombinant polypeptides having UDP-glycosyltransferase activities, including a 1,2-19-O-glucose glycosylation activity and a 1,2-13-O-glucose glycosylation activity for synthesizing of steviol glucosides, are provided. A method of producing a steviol glycoside composition using such recombinant polypeptide is also provided. Also disclosed are steviol glycosides referred to as rebaudioside Z1 and rebaudioside Z2.