  We revisit the cubic interaction of IIB string theory in the maximally
supersymmetric pp-wave background. In the supergravity limit, we show that
detailed comparison with AdS supergravity determine the vertex completely.
Extension of this supergravity vertex to the full string theory leads to a new
cubic vertex that combines the previous proposals and contains additional
terms. We give an alternative derivation of the holographic duality map in
supergravity, first found by Dobashi and Yoneya (hep-th/0406225) and show that
our new vertex is consistent with it. We compare some non-BPS amplitudes
(including impurity non-preserving ones) with the corresponding field theory
correlators, and discuss what they imply for the stringy generalization of the
duality map. We also notice that our vertex realizes the U(1)_Y symmetry
linearly, and propose a similar modification for the flat space vertex.
