Apple has sent an e-mail message to registered developers, telling them that on Jan. 6 — when the Mac App Store launches — the Mac OS X Downloads site will no longer offer apps.

Apple tells developers to submit their software to the Mac App Store instead. Said store “will be the best destination for users to discover, purchase, and download apps,” the company says.

Craig Federighi, vice president of engineering for OS X, demoed Lion at the Back to the Mac event in October. The Mac App Store brings the Apple App Store experience to Mac OS X, making discovering, installing and updating Mac apps easier than ever, he said. Like on the iPad, you purchase apps using your iTunes account and they download and install in just one step.

The Mac App Store will be available for Mac OS X 10.6 (“Snow Leopard”) on Jan. 6. And it will be built into next year’s Mac OS X Lion.