American Railcar Industries Inc , controlled by activist investor Carl Icahn, offered to buy rival railcar maker Greenbrier Cos Inc for $20 per share in cash, valuing the company at about $543 million.

The offer represents a premium of 5.4 percent to Greenbrier's closing price on Monday.

Icahn reported a 9.99 percent stake in Greenbrier last month, making him the company's largest shareholder.

Icahn Enterprises said in a regulatory filing on Tuesday that it had talks with Greenbrier that resulted in the offer for the railcar maker. (http://link.reuters.com/ceg74t)

(Reporting by Sagarika Jaisinghani in Bangalore)