Spark Therapeutics Inc., a locally founded gene-therapy company recently acquired by pharmaceuticals giant Roche, is said to be in a deal to fully occupy a second building across Market Street from what will be its future University City headquarters at the former Bulletin newspaper building.

Owner Brandywine Realty Trust is converting the 64,000-square-foot building at 3000 Market St. into life-science offices where Spark will be the sole tenant, according to a person familiar with the lease negotiations who wasn’t authorized to discuss them publicly.

Brandywine chief executive Jerry Sweeney said during a conference call with analysts Thursday that the building would be leased by “a well-known tenant in the Philadelphia area ... in the cell- and gene-therapy business,” but did not identify the tenant by name.

Spark spokesperson Kevin Giordano said the company has “ambitious growth plans,” but declined to comment on specific locations.

“Spark is working with Roche to assess opportunities to expand our footprint within the city,” he said.

A Brandywine spokesperson declined to share additional details.

Spark, which was founded by researchers at the Children’s Hospital of Philadelphia, was acquired by the Basel, Switzerland-based Roche Group in December. It had already been slated to move into the one-time Bulletin building at 3001 Market St., which the developer is in the process of renovating. Brandywine owns that, too.

The 283,000-square-foot former newspaper building stands to the west of 30th Street Station, across from a public plaza that Brandywine transformed from a parking lot. The building will be Spark’s headquarters when work there is completed by early fall.

The 3000 Market St. building across the street is currently home to the Market Tavern bar, and formerly housed a branch of the for-profit college Brightside Career Institute. Brandywine plans to spend $25.2 million renovating that building, with work scheduled for completion during the first three months of 2021, it said in a financial report on its website.

Brandywine is Philadelphia’s dominant office landlord. It also has a major presence in Austin, Texas, and in the Washington, D.C., area. The former Bulletin building and the 3000 Market St. property are both part of what the company has coined its Schuylkill Yards development, which is seen as eventually comprising five million square feet of offices, homes, shops, and hotel rooms across 14 acres in University City.

Brandywine is working on plans for its first two new buildings at the project site, both of which would rise along the north side of John F. Kennedy Boulevard, west of the train station. One is a tower at 3025 John F. Kennedy Blvd., with 200,000 square feet of offices and 326 apartment units. The other highrise, at 3001 John F. Kennedy Blvd., would comprise 775,000 square feet of offices.

Brandywine had begun working to renovate 3000 Market St. for life-science use before securing Spark as a tenant because it saw demand for that kind of space growing at a faster pace than it could deliver in one of the new towers, Sweeney said.

“We really did see a tremendous growing demand from cell- and gene-therapy companies in Philadelphia,” he said. “The time to build these bigger buildings put us at risk of losing some of that.”

The planned completion dates for renovations at the former Bulletin building and at 3000 Market St. account for delays from required work stoppages due to the coronavirus, Brandywine said. Pennsylvania Gov. Tom Wolf said Wednesday that construction could resume statewide on May 1.

The company said that, in its existing buildings, the pandemic has prompted some tenants to ask for rent relief. Most of those requests have come from retail and coworking tenants, each of which makes up about 2% of Brandywine’s billings, it said.

The company had been able to collect 95% of rents due for April, it said.