GO:0097363:   protein O-GlcNAc transferase activity
Catalysis of the reaction: UDP-N-acetyl-D-glucosamine + [protein]-L-serine = UDP + [protein]-3-O-(N-acetyl-D-glucosaminyl)-L-serine, or UDP-N-acetyl-D-glucosamine + [protein]-L-threonine = UDP + [protein]-3-O-(N-acetyl-D-glucosaminyl)-L-threonine.