Mutation of the major 5' splice site renders a CMV-driven HIV-1 proviral clone Tat-dependent: connections between transcription and splicing.

Efficient transcription from the human immunodeficiency virus type 1 long terminal repeat (HIV-1 LTR) promoter is dependent on the viral transactivator Tat. To generate a Tat-independent proviral plasmid, we replaced the promoter in the HIV-1 LTR with the immediate early promoter of cytomegalovirus. Transfection of this plasmid yielded Tat-independent production of infectious HIV-1. Tat-independent expression was lost, however, when the major 5' splice site in the HIV-1 genome was mutated and no HIV-1-specific RNA or protein was detected. This defect was restored when a Tat expression plasmid was cotransfected. Our results support recent reports indicating an influence of the recognition of splice sites on efficient transcriptional elongation.