No successor has been named.
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There also has been a move away from star anchors.
Other high-profile personalities also have left, includingChuck ToddfromNBC News,Chris Wallacefrom CNN andHoda KotbfromToday.
Lester HoltHeidi Gutman/NBCU Photo Bank/NBCUniversal via Getty Images
Quite simply, Lester is the beating heart of this news organization, she wrote.
Holt became permanent anchor ofNightly Newsfollowing the suspension of Brian Williams from the broadcast.
Williams was in the midst of controversy over the embellishment of an account of his experiences reporting from Iraq.
ABCsWorld News Tonighthas topped the ratings in total viewers for the past eight seasons, withNBC Nightly Newsin second.
Here is Holts note to staffers today:
Hello to all my Nightly News and Dateline colleagues.
I want to share with you a big decision I have made about my future at NBC News.
