The term "RJ45" is 1980's terminology, but I think that I understand what you mean. An RJ45 can never support a T1 or PRI circuit. You are speaking of 8P/8C plugs and jacks, right? In essence, all that you need is a two cable pairs rated at CAT1 or better for a run up to 166 feet. If the run is longer, then go ahead and run a CAT5 or better for each circuit to play it safe.
As previously mentioned, a T1 or PRI circuit only uses pins 1,2,4 and 5 on the plug or jack to provide a transmit and receive path. Other pairs are not necessary. The jack at the far end should be equipped with shorting bars to provide loopback when the hardware is not connected (RJ48 wiring pattern) in order to keep the circuit alive if testing is necessary.
Chances are, you can get away with a simple CAT5e cable run, terminated either 568A or B wiring patterns. They must be the same at both ends.
Here are some reference links to give you some insight into the difference between an RJ45 and RJ48 wiring patterns.
RJ48 Wiring diagram RJ45 Wiring diagram Here's another link to most other jack wiring diagrams:
Other USOC Wiring patterns in general