What to write in the followup email to a professor for a graduate teaching assistantship I will be pursuing masters from UT Austin this fall.I have mailed professors for the position of  a teaching assistant. Some of them replied and some did not. 
What should I write in the followup email to the professors who did not respond.

Thanks!
In such situations, it is always beneficial to give them the benefit of the doubt and assume that they have either (1) not seen your email or (2) seen it, but forgot to reply. Seeing that many academics are busy, let's assume that with such schedules any of the above two options are viable. 

You can perhaps write something to the effect of "...I am writing to you once again, because I don't think you have received my earlier email...". 

Good luck!