They may form Regimental Combat Teams or not, depending on the mission given at the time. For example, 1st Marine Division was task organized differently from how the 2d Marine Division was organized for the invasion of Kuwait in 1991. One of the interesting differences between the two divisions in the desert is that 2d MarDivb had one of its regiments afloat forming an RCT in a MEB and it was replaced by a US Army brigade detached from an army division. And the 10th Marine Regiment had three of its own battalions assigned to it (the other battalion was afloat with the MEB) as well as a battalion from 12th Marines (3d Marine Division), an army SP artillery battalion as well as a rocket battery. And you are correct there are no T/O brigade organizations in a Marine Division. There are separate brigades, Marine Expeditionary Brigades, formed around one infantry regiment which would be a Regimental Combat Team. However they are task organized to fulfill the mission requirements.

Sincerely,
Kevin