it;s not NTA directly : 

nupic@nupic-vm:~/nupic-source/build$ echo $NTA
/home/nupic/nta/eng/
nupic@nupic-vm:~/nupic-source/build$ echo $PYTHONPATH
/home/nupic/nta/eng//lib/python2.7/site-packages

 export PYTHONPATH=${PYTHONPATH}:${NTA}/lib/python<<how we reference python version here?>>/site-packages