Sequence nodes tell the exporter how to export animation data over a given range of frames in Maya. They are required if animation is to be exported. The sequence node contains a variety of information such as the name of the animation sequence, start and end frames, cycling and blend information, and frame rate. See the section on Sequence Node Parameters (coming soon) for more details about sequence objects.
Sequence Nodes are actually just empty group objects with custom attributes added to them. The naming convention for sequence nodes is Sequence_name. Sequence nodes must always be prefixed with Sequence_, otherwise they will not be exported. Sequence nodes can be created and edited manually, but it is far easier to create them from the dtsUtility window.