Image courtesy SGA

Boston-based Leggat McCall Properties and DLJ Real Estate are proposing a 1.1 million-square-foot mixed-use development in Somerville’s Boynton Yards, where the developers already have begun construction of a speculative life science building.

The master-planned development would comprise nearly 1 million square feet of office-lab space, 338,000 square feet of multifamily housing, 42,500 square feet of retail and civic space and 1,000 underground parking spaces, according to an application submitted to the city of Somerville.

The 320-unit housing component includes 64 income-restricted units, complying with Somerville’s 20 percent affordable housing requirement for new developments. Two acres would be reserved for open space and civic uses.

Developers estimate the project would create 4,000 permanent jobs. The site on South, Ward, Harding and Earle streets contains a mix of commercial and industrial buildings and surface parking, including a 3.1-acre parcel that the developers acquired last fall from Gentle Giant moving company for $23 million.

In December, Leggat McCall broke ground on a speculative 9-story, 289,000-square-foot lab building at 101 South St., also in partnership with DLJ Properties. That building is included in the master-plan application.

The Boynton Yards section near Union Square has attracted new real estate investors and tenants in anticipation of the MBTA Green Line Extension project, which brings a Green Line station to Prospect Street in 2021, and its proximity to East Cambridge’s massive tech and life science cluster.

The project poses competition for the neighborhood’s other major developer, US2, which is overseeing the 2.3 million-square-foot Union Square redevelopment program including a 175,000-square-foot office-lab building at Prospect Street and Somerville Avenue in the initial phase of construction.