Union Bank of California has signed downtown’s biggest lease deal this year, taking 345,000 square feet of office and retail space at Union Bank Plaza, where it has long maintained its Los Angeles headquarters.

The bank, a subsidiary of San Francisco-based UnionBanCal Corp, renewed and extended its occupancy “long term” at the 445 S. Figueroa St. tower, according to a statement released Monday by Hines, a Houston-based developer that owns the property.

The extension includes a two-floor expansion at the 39-story tower. Hines claimed the deal is the largest office lease transaction downtown since 1989. Union Bank has occupied the 637,000-square-foot building since it opened in 1967.

Hines has been active in the downtown market. It recently paid $285 million for the iconic Citigroup Center, known as the “L.A. Law” building.

The lease rate was not disclosed, but recently rents have softened. The average downtown Class A asking rent in the third quarter was $3.23 per square foot per month, down a penny from the second quarter, according to Grubb & Ellis Co