On resume do I list my "official" responsabilities or actual?

I am working to update my resume and I am following the advice out of the resume workbook from MT.  The thing I am struggling with is the responsibilities in my current job.

My actual job is a Senior Developer (programmer), but I have been working as a project lead for the last year.  I am responsible for 4 developers and I am pretty much working full time just on the management side (And have been for about a year).

That being said, I am concerned that accomplishments will in no way match what is in my responsibilities.  So do I list what I am actually responsible for, or what my job description says I am responsible for?

Thank you for any advice!