NEW YORK (AP) — Books and bits united Monday as Microsoft provided an infusion of money to help Barnes & Noble compete with top electronic bookseller Amazon. In exchange, Microsoft gets a long-desired foothold in the business of e-books and college textbooks.

With Microsoft Corp.'s $300 million investment, the two companies are teaming up to create a subsidiary for Barnes & Noble's e-book and college textbook businesses. Microsoft is taking a 17.6 percent stake in the venture.

The agreement underscores the importance of electronic bookstores as traditional booksellers and technology companies jockey for position in the increasingly competitive market. While no definitive numbers exist, e-books are believed to account for some 20 percent of book sales in the U.S.

For Microsoft, the investment is a way to get back into the e-book business. It has dabbled in the field since at least 2000, but never developed much traction. It was Amazon that blew the market open with the 2007 launch of the Kindle, creating a potent challenge to Barnes & Noble's brick-and-mortar bookstores.

Major Microsoft competitors Apple and Google now have their own e-book stores. All three companies are building businesses that encompass hardware, software and content in an "ecosystem," and e-books and readers are part of the puzzle.

With that perspective, the deal is very important, said Walter Pritchard, an analyst with Citigroup. But he doesn't expect any near-term financial impact from the deal, noting that even if the Microsoft-Barnes & Noble venture is successful, it leaves the Nook a distant second in the e-reader market, behind the Kindle.

The deal gives Barnes & Noble ammunition to fend off shareholders who have agitated for a sale of the Nook e-book business or the whole company, but the companies said Monday that they are exploring separating the subsidiary, provisionally dubbed "Newco," entirely from Barnes & Noble. That could mean a stock offering, sale or other deal.

The deal also puts to rest concerns that Barnes & Noble doesn't have the capital to compete in the e-book business with market leader Amazon.com Inc. and its Kindle, said analyst David Strasser at Janney Capital.

Barnes & Noble Inc.'s stock zoomed up $7.07, or 52 percent, to close trading at $20.75. The opening price of $26 was a three-year high. Microsoft's stock rose 4 cents to $32.

The investment also means that Microsoft will own part of a company that sells tablet computers based on Google Inc.'s Android, one of the main competitors of Windows Phone 7, Microsoft's smartphone software.

Microsoft also said the deal means that there will be a Nook application for Windows 8 tablets, set to be released this fall. The app is likely to get a favored position on Windows 8 screens.

There's already a Nook application for Windows PCs, but none for Windows phones.

William Lynch, the CEO of Barnes & Noble, said Nook software will continue to be available on devices like the iPhone that compete with Windows Phone.

He declined to say whether it was Barnes & Noble or Microsoft that initiated the discussions, but he said the talks had been going on since before the beginning of the year.

"We have been circling the relationship for quite a long time," added Microsoft president Andy Lees. "When you think of different types of reading and what's going to happen when that goes digital, it's really quite dramatic to be bringing that to Windows customers."

The Nook has pleasantly surprised publishers, who worry about Amazon's domination of the e-market. Unveiled to skeptical reviews in 2009, the Nook is estimated to account for about 25 percent of the U.S. e-book market. The Nook helped to cut Amazon's share from what was believed to be 90 percent to around 60-65 percent. David Pogue in The New York Times called the initial device "an anesthetized slug," but praised the new Nook Simple Touch as a "very big deal" that offers "spectacular, crisp pages to read in any light."

Barnes & Noble investors have also been concerned about the recent government lawsuit against Apple and some leading publishers over alleged price fixing. When Apple launched its iPad in 2010, Simon & Schuster, Penguin Group (USA) and other publishers switched to an "agency" model that allowed publishers to set prices for e-books, a system many believe helped Barnes & Noble.

Amazon had been offering top-selling e-books for $9.99, a cost publishers, agents and writers believed was so low it could drive competitors out of business. Three of the five publishers sued— Simon & Schuster, HarperCollins and the Hachette Book Group — have already agreed to settle, meaning prices for their e-books likely will again drop on Amazon.

Microsoft has a long-standing interest in the e-book field. It launched e-book software in 2000, but was never able to build a substantial library of books. It's discontinuing the software on Aug. 30.

Barnes & Noble, based in New York, currently runs 691 bookstores in 50 states. The companies said that the subsidiary will have an ongoing relationship with Barnes & Noble's retail stores, but what that relationship will be is unclear.

"The whole reason the Nook business is expanding so rapidly is because bookstores are committed to it and know how to market the product in that environment," said Michael Norris, an analyst at Simba information.

The possibility of a separation of Barnes & Noble's digital and college businesses has been brewing.

In January, Barnes & Noble said it was considering options for its Nook business, including possibly spinning it off or expanding overseas, and said it expected the review to be complete by the end of the year.

And in March, private investment firm G Asset Management, a Barnes & Noble shareholder, offered $460 million for a 51 percent stake in the company's college bookstore unit, Barnes & Noble College Booksellers LLC.

Under that plan, the college bookstore unit was proposed to begin as a private business but become public within a "reasonable" amount of time. G Asset's offer was contingent upon Barnes & Noble keeping current management in place and separating its Nook e-business from the rest of the company. At the time the offer was made, Barnes & Noble declined to comment.

In 2009, Barnes & Noble Inc. bought the college bookstore unit from Chairman Leonard Riggio in a deal worth $596 million. The deal ended up costing Barnes & Noble $460 million after accounting for the unit's cash on hand at the closing date.

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AP Retail Writer Mae Anderson, Business Writer Michelle Chapman and AP National Writer Hillel Italie contributed to this report.