Eukaryotic layered vector initiation systems

A DNA vector comprising, in a 5′ to 3′ orientation,

• a promoter sequence that initiates RNA synthesis in a eukaryotic cell, a sequence that initiates transcription of alphavirus RNA, a sequence that encodes biologically active alphavirus nonstructural proteins, a sequence comprising an alphavirus junction region promoter, a sequence heterologous to alphavirus sequences, and a sequence comprising an alphavirus RNA polymerase recognition sequence.