Berkeley Investments has secured Sasaki’s Watertown office for $23M with lab conversion aspirations for the 97K SF building.

The developer bought Sasaki’s longtime headquarters at 64 Pleasant St. near Watertown Square last week, the architect announced. Berkeley announced renovation plans to attract small and midsize life sciences companies to the suburb that has become an alternative to the airtight Kendall Square.

“Historic buildings are home to a range of features that are attractive to life sciences companies, and we see great synergy between the needs of the market and the benefits this building provides,” Berkeley President Young Park said in a statement.

Sasaki will be involved in Berkeley’s design process as the firm, which has called the historic mill site on the bank of the Charles River home since the 1970s, is on the cusp of securing a new Boston headquarters, CEO James Miner said in a statement.

The price was undisclosed, but Middlesex County records show the deed transfer for $23M and a $17.5M mortgage to Berkeley from BayCoast Bank. Hunneman brokered the deal.

Berkeley plans to update the 150-year-old building with energy-efficient upgrades and new architectural elements, including higher ceilings. SGA will lead the design team and partner with Sasaki on repositioning the building, which sits a few miles across the Charles River from Allston, where Berkeley was selected by Harvard to develop 548K SF of lab-ready office space with retail, residential and open-space components. That project is undergoing city review.

Berkeley’s new Watertown project will add more supply to the growing Watertown market, where several developers are building life sciences spec and pre-leased projects.