A biotech tenant in one of Alexandria Real Estate Equities' Cambridge buildings is leaving for another of the REIT's properties in Watertown.

Foghorn Therapeutics signed a roughly 73K SF lease at 99 Coolidge Ave. in Watertown, according to a Securities and Exchange Commission filing.

The 255K SF property is a redevelopment of the former Mount Auburn Club fitness club. Alexandria owns 75.7% of the property, in partnership with National Development, according to Banker & Tradesman, which first reported the deal.

Foghorn will pay $3.9M to occupy 45K SF in the first year and then $5.2M the second year for 60K SF, the SEC filing says. It will then pay $6.3M starting in October 2027 for the full 73K SF, with a 3% annual increase for each remaining year.

Cambridge-based Flagship Pioneering founded Foghorn in 2018, and the company now has 112 full-time employees.

It had previously taken up 81K SF at Alexandria's 500 Technology Square in Cambridge. Before that, it had been housed in 21K SF at 100 Binney St., the Boston Business Journal reported.

An entity linked to Alexandria acquired the 6.3-acre site in Watertown for less than $33M in July 2020, according to Wicked Local. The owner of the club, the Crowley Family, closed it, citing the pandemic as the reason to sell.

The new building on the site is also home to Sonata Therapeutics and Revival Cafe + Kitchen.

With the glut of new lab space in Greater Boston, tenants have been attracted to purpose-built life sciences space rather than conversions and "subpar" lab buildings, developers said at a Bisnow event last month. With vacancy climbing to 25% in Q1, according to CBRE, tenants have had the upper hand and have been picky about the type of space they lease.