Updated from 12:02 p.m. ET

Abigail Johnson, daughter of

Fidelity

Chairman Ned Johnson, will replace Bob Pozen at the head of the nation's largest fund company on June 15. The move is noteworthy because of the firm's size, but shouldn't lead to sweeping changes.

The Boston fund behemoth, which has more than $900 billion in assets under management, issued a news release just before midday. The 39-year-old Johnson will assume Pozen's post as president of

FMR

, the sprawling firm's money-management arm. The decision ends rampant speculation about when or if Johnson, a former investment analyst and fund manager who's been with the firm since 1988, would oversee the privately held firm's money managers, traders and analysts.

"From a structural standpoint, this is the biggest news to come out of Fidelity in many years," says Jim Lowell, editor of

Fidelityinvestor.com

, an independent newsletter. "This confirms the idea that Abigail is taking over the company. She's stepping from behind the management curtain into a very public position."

During her career, Johnson has run Fidelity's

(FSDCX) - Get Report

Select Developing Communications,

(FSTCX) - Get Report

Telecommunications,

(FTRNX) - Get Report

Trend and

(FDGFX) - Get Report

Dividend Growth funds. Her tenure as an analyst and portfolio manager lasted nine years, ending in 1997 when she began overseeing stock-fund managers.

"While she wasn't the top-performing manager at any given time, she was slightly above average," says Lowell. "She's clearly had a carefully calibrated career."

Currently Johnson is an associate director and senior vice president, overseeing the firm's growth and capital appreciation funds while also leading several technology initiatives for the firm.

While Johnson's ascension is noteworthy, it's unlikely to lead to sudden or drastic changes.

"She'll do absolutely nothing in her first three months," says Lowell. "Her first 100 days will be like

President Bush's

: She'll lay low."

That makes sense, given the firm's solid returns. The firm's U.S. stock funds rode the hot tech and telecom sectors to solid gains in the tech-led bull market of 1998 and 1999. But more than 70% of the firm's direct-sold U.S. stock funds topped the

S&P 500

last year, when the tech sector fund, according to

Morningstar

.

Through the start of this month, two-thirds of the firm's direct-sold U.S. stock funds topped their average peer over the past five years.

"I'll have my own mark on certain things, but I've been part of the management team for the last four years," Johnson said in a conference call. Johnson also weighed in on two other key matters: She doesn't expect her father to retire anytime soon and she eschewed the idea of the company having an initial public offering.

Pozen, 54, assumed his post four years ago. The firm's assets rose from some $400 billion to $900 billion on his watch. Insiders have hinted that his interest in broader political issues has given him a hankering to work in Washington. A recent appointment by President Bush to a commission to reform Social Security triggered Pozen's decision to leave the firm.

Pozen will leave the firm at the end of the year, the company said.