Integration of rous sarcoma virus DNA: a CA dinucleotide is not required for integration of the U3 end of viral DNA

Abstract

The two ends of RSV linear DNA are independently inserted into host DNA by integrase in vivo. We previously showed that the range of U3 sequences that are acceptable substrates for integrase appeared to be greater than the range of acceptable U5 sequences in vivo. We have done additional experiments to determine which U3 sequences are good integrase substrates. On the U3 end, there does not appear to be a stringent requirement for the canonical CA, integrase can efficiently remove three nucleotides, and six nucleotides are sufficient to allow integration with reasonable, albeit reduced, efficiency.

FIG. 1.

Structure of the RSVP vectors. (A) The PPT (white letters with a shaded background) and U3 sequences of wild-type RSV and the various mutants are shown. Mutations are underlined. The complete descriptions of the titers for each mutant are given in reference . (B) Schematic numbering of the nucleotide positions in the ends of the provirus. The last nucleotide on each end of a normal provirus is number 1. (C) Cleavages of the mutant PPTs by the RNase H of RSV reverse transcriptase. (Data are from reference .) The positions of the cleavages are inferred from the sequences of 2-LTR circle junctions isolated from cells infected with the viruses carrying the mutant PPTs. The arrows depict the positions of the predominant RNase H cleavages. Mutated sequences are shown in white letters with a shaded background.