From: http://www.promega.com/figures/frame.asp?fn=0286VC

What is T7?

1. The cleavage site of T7ase which is located at the begining of the multiple cloning site.
2. The T7 polymerase promoter just prior to the multiple cloning site.
3. A reporter gene which is disrupted if a fragment of DNA is inserted into the multiple cloning site.
4. The beginning of the origin of replication.