LAS VEGAS (AP) — Sports betting website DraftKings Inc. is buying the online gambling subsidiary of Golden Nugget Inc. in a stock deal valued at $1.56 billion. The two companies said Monday that the acquisition of Golden Nugget Online Gaming gives Boston-based DraftKings a well-known brand in the casino and gambling world, and adds more than 5 million customers to DraftKings iGaming accounts. Tilman Fertitta, the Houston-based billionaire owner of Golden Nugget Online Gaming, also owns the NBA Houston Rockets, Landry’s restaurants and Golden Nugget casinos in Las Vegas and Atlantic City, New Jersey. He pointed to promotional and marketing advantages for the two publicly traded companies.