CHICAGO-Motorola Mobility, the cell phone/tablet spin-off from the main Motorola firm now owned by Google, has agreed to become the largest tenant at Merchandise Mart in the downtown. The firm will take almost 600,000 square feet on the top four floors of the Vornado Realty Trust-owned property.

The 3.5-million-square-foot building was built in 1930, and is one of the largest commercial buildings in the world. This transaction increases the office component of the building to more than 1.7 million square feet, “continuing the right sizing of the mix of office space and showroom space,” according to a Vornado statement.

The property is in the recently-popular River North area, previously known for an increasing number of restaurants and night clubs, and new residential buildings, now becoming one of the hottest office markets in the city. Hines has partnered with the Kennedy family and Magellan to re-launch a $1 billion office-multifamily complex nearby.