A novel subgenomic murine leukemia virus RNA transcript results from alternative splicing

Here we show the existence of a novel subgenomic 4.4-kb RNA in cells infect ed with the prototypic replication-competent Friend or Moloney murine leuke mia viruses (MuLV). This RNA derives by splicing from an alternative donor site (SD') within the capsid-coding region to the canonical envelope splice acceptor site. The position and the sequence of SD' was highly conserved a mong mammalian type C acid D oncoviruses. Point mutations used to inactivat e SD' without changing the capsid-coding ability affected viral RNA splicin g and reduced viral replication in infected cells.