Locking and atomic commitment are two fundamental problems underlying transaction management in fault-tolerant distributed systems. In this paper we discuss these problems in the context of an asynchronous system with replicated objects. We present a generic primitive, named Dynamic-Terminating-Multicast (or DTM) of which instances enable to implement a locking protocol and an atomic commitment protocol. By unifying the mechanisms needed to implement these protocols, we believe that the DTM primitive can be considered as a basic building block of distributed transactional systems. We show that this primitive can be implemented in an asynchronous system based on an unreliable failure detector.