UAL Corp ( UALAQ), the parent company of United Airlines, and Atlantic Coast Airlines ( ACAI) said the regional carrier no longer would be providing service under the Chicago-based carrier's United Express Service. The service between Chicago's O'Hare and Washington's Dulles airports will be assumed bynew and existing partners, UAL said. United, which is currently operating under Chapter 11 bankruptcy protection, did not give a reason for the change, saying only that it was "ending its relationship" with Atlantic Coast Airlines and that it now has "the opportunity to improve the flight experience with United Express for our passengers." Atlantic Coast said it had "reached an agreement with United Airlines providing for an orderly transition and exit plan for all its United Express aircraft as a result of United's decision to reject its agreement with ACA..." UAL said Chautauqua Airlines, Republic Airlines and Shuttle America, newly announced partners in the service, will operate United Express service out of Dulles and O'Hare, while existing partners Air Wisconsin, Trans States and Mesa Air ( MESA ) also will serve O'Hare and Dulles. SkyWest ( SKYW ) also will serve O'Hare. Air Atlantic said the transition is scheduled to begin June 4 and continue through Aug. 5. The Dulles, Va.-based carrier said the agreement "clears a significant hurdle" in its transition "from a fee-per-departure carrier to its new identity as Independence Air," a low-fare airline serving Dulles, which will be officially launched in May. The new service arrangement is subject to approval by the U.S. Bankruptcy Court now handling UAL's chapter 11 case, and is expected to be considered April 16.. Atlantic Coast shares rose 2 cents, or 0.3%, to $7.16, UAL shares were unchanged at $1.53, Mesa shares rose 15 cents, or 1.8%, to $8.60 and SkyWest's fell 13 cents, or 0.7% to $19.30. .