  We study the effect of all matter multiplets contained in {\bf 27}
representation of $E_6$ GUT on gauge coupling unification in extra dimensions.
Extra members of {\bf 27} multiplets of all three generations have their `zero
modes' near $m_t$ such that they can be directly probed. From TeV scale onwards
extra dimensions open up, theory becomes N=2 supersymmetric and gauge couplings
unify or they do not, depending on how we distribute matter fields and gauge
fields in bulk and brane. We find three such possible embedding which will lead
to perfect gauge coupling unification below 100 TeV region for one extra
dimension and lower than that if number of extra dimensions is larger.
