The UK's Transport for London (TfL) has completed its acquisition of Tube Lines.
Tube Lines has transferred from shareholders Bechtel and Amey to become a wholly owned subsidiary of TfL.
The arrangement is expected to give TfL greater flexibility in managing upgrade programmes alongside other improvements being delivered across the network.
London Mayor Boris Johnson said the deal marks a new era for the Tube.
"We have wasted no time in acting to limit the disruption of the Tube upgrade programme by cutting back the closures previously planned for this summer, and we will now look at how we can keep disruption to a minimum," Johnson said.
Tube Line manages the maintenance, renewal and upgrade of rail infrastructure of the Jubilee, Northern and Piccadilly underground lines.
Amey will continue to provide management and maintenance services on the lines on an ongoing basis.