One federal prosecutor in Manhattan is being promoted to become the new chief of the public corruption unit, while another is departing to join Robert S. Mueller III, the special counsel overseeing the investigation into Russia’s meddling in the 2016 presidential election.

The new chief of the corruption unit in Manhattan is Tatiana R. Martins, who in 2015 helped to convict Dean G. Skelos, the Long Island Republican who was the majority leader of the State Senate until shortly after his arrest that year.

Ms. Martins, the deputy chief of the unit, succeeds Andrew D. Goldstein, who will join Mr. Mueller’s team after having led the public corruption unit for about a year.

As a line prosecutor, Mr. Goldstein was a member of the team that in 2015 won the conviction of Sheldon Silver, a Manhattan Democrat who had been the longtime speaker of the State Assembly.