PALO ALTO, Calif., and TOKYO — Telsa Motors and Toyota Motor Corp. officially signed an agreement late last week stemming from a May announcement. That's when they revealed collaboration toward development of an electric version of the Toyota RAV4.

Tesla's Elon Musk and Toyota's Akio Toyoda are aiming for their companies to bring an electric version of this vehicle to the U.S. market in 2012.

They indicated prototypes will be made combining the RAV4 model with a Tesla electric powertrain. Tesla plans to produce and deliver a fleet of prototypes to Toyota for evaluation within this year.

The companies indicated the first prototype has already been built and is now undergoing testing.

Back in May, Tesla and Toyota initially unveiled their intent to cooperate on the development of electric vehicles, parts and production system and engineering support.

Tesla maintains that it seeks to learn and benefit from Toyota's engineering, manufacturing and production expertise. Meanwhile, Toyota contends its objective is to discover more from Tesla's electric vehicle technology, daring spirit, quick decision-making and flexibility.

"Toyota has, since its foundation in 1937, operated under the philosophy of ‘contributing to society through the manufacture of automobiles,' and made cars that satisfy its many customers around the world," the automaker insisted.

Furthermore, Tesla reiterated that its intention is "to produce increasingly affordable electric cars for mainstream buyers — relentlessly driving down the cost of electric vehicles."

Beyond the RAV4 development, Tesla and Toyota became integrated in other ways, too.

The companies also revealed back in May that Toyota had agreed to purchase $50 million of Tesla's common stock issued in a private placement.

And in a related development, Tesla bought the former NUMMI factory in Fremont, Calif., a plant formerly utilized by Toyota. Tesla intends to build the Model S sedan and other future vehicles at the facility.