A new joint venture between Cousins Properties, Riverside Resources and Ironwood Real Estate will put a fully leased 31-story office tower on the site of the former Sullivan's Steakhouse at 300 Colorado.

The announcement could signal a shift in downtown development from residential to office space. The site, owned by Riverside Resources and Ironwood Real Estate, originally was envisioned as a 44-story multifamily tower. Now, working with Cousins, it will be a $175M tower with 300K SF of office space, occupied by Parsley Energy.

“Making this transaction happen required the persistence, creativity and cooperation of many different parties, and we truly appreciate the efforts of everyone involved,” Riverside Resources co-founder Don Reese said in a statement. “We certainly intend to build an enduring office tower that will make all those parties and Austin proud.”

Parsley Energy, a midsize player in the fracking industry, moved to Austin in 2014, about the same time the company went public. CEO Bryan Sheffield told the Austin Business Journal the move of its headquarters from Midland to Austin had made it far easier to hire highly skilled engineers.

Across the street from the proposed tower site, Parsley was one of the first major tenants in Cousins' 30-story Colorado Tower. Parsley intends to maintain its 135K SF lease in Colorado Tower through 2022, and occupy the entire 300K SF new tower, known as 300 Colorado.

If all goes as planned, that would make Parsley Energy the largest downtown Austin business tenant. Google has about 300K SF, followed by Facebook with 231K SF and Whole Foods with 134K.

The 31-story tower will be 18 stories of office space on top of a 13-story garage, according to the  Austin American-Statesman. The project will break ground in December and be completed by 2022.

Downtown, Cousins has developed both Colorado Tower and the Frost Bank Tower. Riverside Resources developed the 16-story apartment tower, the Whitley, and is constructing a condo high-rise, Fifth & West.

On the current site at 300 Colorado, Sullivan's Steakhouse and Sully's Side Bar close Jan. 9, according to Austin Eater.