Nuclear NMNAT isoform. Catalyzes the formation of NAD+ from nicotinamide mononucleotide (NMN) and ATP. It can also use the deamidated form of nicotinic acid mononucleotide (NAMN) as substrate with the same efficiency. Interacts with PARP-1/ARTD1. Protects against axonal degeneration following mechanical or toxic insults. Widely expressed.