Wall Street became increasingly skittish about Rupert Murdoch’s prospects for clinching a deal to buy Dow Jones & Co., sending the stock of the Wall Street Journal publisher down more than 5% yesterday as a deadline arrived for the Journal’s controlling shareholders to make a decision.

Members of the Bancroft family, which has controlled Dow Jones for a century, had a 5 p.m. deadline yesterday to tell the family’s lead trustee how they would vote on Mr. Murdoch’s $5 billion offer to buy the company. A Bancroft family spokesman declined to comment on the vote’s outcome late yesterday.

The next expected step is for News Corp., Mr. Murdoch’s press and broadcast conglomerate, to be informed of how many Bancroft family members were in favor of the offer and decide whether it has enough support to proceed.

Yesterday, a News Corp. spokesman said the company was “highly unlikely” to go ahead with the deal if the level of support among the Bancrofts remained at just 28% of the shareholder vote, which the Wall Street Journal reported was the level of commitment as of Sunday.

The News Corp. spokesman asked not to be named due to the sensitive nature of the discussions. News Corp. has said it wants sufficient support from the Bancrofts to avoid a potential messy showdown later.

The Bancrofts collectively control 64% of the shareholder vote of Dow Jones through a special class of stock, but only about half of them need to support the deal for it to succeed.

The Bancrofts are a diverse clan, and their voting interest in the company is held through a complex series of privately held trusts, making the outcome difficult to predict.

Over the past few weeks, investors have been steadily pushing Dow Jones shares below the $60 price that Mr. Murdoch has offered, reflecting increasing doubts about the deal going through.