  A nonperturbative renormalization group equation describes how the momentum
dependent four-quark vertex depends on an infrared cutoff. We find a quasilocal
one-particle irreducible piece generated by (anomaly-free) multi-gluon
exchange. It becomes important at a cutoff scale where scalar and pseudoscalar
meson-bound states are expected to play a role. This interaction remains
subleading as compared to the effective one-gluon exchange contribution. The
local instanton induced four-quark interaction becomes dominant at a scale
around 800 MeV. In absence of a gluon mass the strong dependence of the
one-gluon exchange on the transferred momentum indicates that the pointlike
interactions of the Nambu-Jona-Lasinio model cannot give a very accurate
description of QCD. A pointlike effective four-quark interaction becomes more
realistic in case of spontaneous color symmetry breaking.
