  Lepton number as a fourth color is the intriguing theoretical idea of the
famous Pati-Salam (PS) model. While in conventional PS models, the symmetry
breaking scale and the mass of the resulting vector leptoquark are stringently
constrained by $K_L\to\mu e$ and $K\to\pi\mu e$, the scale can be lowered to a
few TeV by adding vector-like fermions. Furthermore, in this case, the
intriguing hints for lepton flavour universality violation in $b\to
s\mu^+\mu^-$ and $b\to c\tau\nu$ processes can be addressed. Such a setup is
naturally achieved by implementing the PS gauge group in the five-dimensional
Randall-Sundrum background. The PS symmetry is broken by boundary conditions on
the fifth dimension and the resulting massive vector leptoquark automatically
has the same mass scale as the vector-like fermions and all other resonances.
We consider the phenomenology of this model in the context of the hints for
lepton flavour universality violation in semileptonic $B$ decays. Assuming
flavour alignment in the down sector we find that in $b\to s\ell^+\ell^-$
transitions the observed deviations from the SM predictions (including $R(K)$
and $R(K^*)$) can be explained with natural values for the free parameters of
the model. Even though we find sizable effects in $R(D)$, $R(D^*)$ and
$R(J/\Psi)$ one cannot account for the current central values in the
constrained setup of our minimal model due to the stringent constraints from
$D-\bar D$ mixing and $\tau\to 3\mu$.
