AUSTIN, Texas (Bloomberg) -- Vignette Corp., a maker of software to manage Web site content, agreed to buy closely held DataSage Inc. for about $553.6 million in stock to add software that personalizes electronic-commerce transactions.

The Austin, Texas-based company said it will exchange 3.16 million of its shares for DataSage. It expects to take charges in the first and second quarters because of the transaction, its largest acquisition ever. Closing is expected by April.Vignette said the acquisition should help it get a larger portion of the electronic-business software market, which analysts expect to grow to $3.7 billion by 2002. DataSage's customers include Amazon.com Inc., Outpost.com, and Sears Roebuck & Co.

DataSage, based in the Boston suburb of Reading, Massachusetts, has about 100 employees and most of them will be moved to Austin, spokesman Michael Berman said. Vignette said it expects to add most of DataSage's employees to its workforce of 800.

DataSage was founded by David Blundin, currently chief executive, in 1997. The status of DataSage's management and whether to close its Massachusetts headquarters are issues currently being considered, Berman said.

Vignette shares rose 8 1/8 to 183 5/16 in midmorning trading. They've risen more than 18-fold since the company first sold shares to the public in February.