The above diagram gives a simplified overview of the responsibilities of each of the roles when steering the current release.  In practice, multiple discussions and iterations may be required to reach agreement.

The Program Manager is responsible to Steer Release Scope. As new business requests arise, the Program Manager either adds them to the program roadmap, or if urgent, creates a new Feature and assigns it to the current release.  This notifies the Enterprise Architect to take the next action.

The Enterprise Architect is responsible to Perform Architectural Analysis.  He/she reviews features that are waiting for architectural analysis ("analysis queue"), and identifies potentially impacted teams.  For each impacted team, he/she creates a size request.

The Team Leads are responsible to Manage scope.  They are notified of the sizing requests and collaborate on the expected work for the Feature.  They create Work Record associated with the Feature, which includes estimates.

The Program Release Manager is responsible to Steer Release Plan.  He/she tracks the state of the release plan, which will become "At Risk" when estimates provided by the teams exceed the projected capacity of those teams.  He/she adjusts the Release Plan (perhaps removing other features, or re-allocating resources) and generates Change Approval Records.

The Team Leads are notified of the Change Approval Records.  Ideally all teams approve all changes, but several iterations may be required to reach agreement. 

Once all the changes have been approved, the Program Release Manager can set the Release Plan to "committed".