  A satisfactory understanding of the origin of the dependence of galaxy
properties on their environment has remained, so far, out of reach. In the
light of numerous observational results and substantial theoretical progress
obtained for clusters of galaxies in the last years, a primary goal is to
understand how the star formation activity depends on cluster substructure,
i.e. on the merging/accretion history of a cluster. In this contribution we
present a case in which it is possible to identify the cluster environment, and
in particular the intracluster medium and the recent infall history of galaxies
onto the cluster, as the cause for an abrupt change in the star formation
histories of a subset of galaxies in the Coma cluster.
