PCR-mediated recombination: a general method applied to construct chimeric infectious molecular clones of plasma-derived HIV-1 RNA.

A PCR-based approach was developed that provides a powerful tool for engineering recombinant molecules without reliance on restriction sites. DNA sequences were first amplified by high-fidelity PCR using Pfu polymerase; they were then used both as 'megaprimers' and templates in subsequent asymmetric long PCR amplifications to form chimeric clones. To demonstrate the technique, we constructed chimeric full-length HIV-1 clones derived from reverse-transcribed plasma viral RNA and proviral LTRs. Biologic characterization of these clones showed that most were infectious in tissue culture and sequence analysis demonstrated an error rate of only one base change in 20 kb of DNA sequence. For PCR-mediated recombination, it is necessary to know the sequence of the 3' and 5' overlapping regions of the desired PCR products. This method may be extended to include construction of chimeras between any DNA fragments lacking sequence homology. Such chimeras may be constructed by introducing overlapping sequences to one of the fragments. To ensure that unwanted mutations have not been introduced into the clones constructed by this method, each clone should be sequenced. Our results demonstrate that by using a high-fidelity polymerase and highly controlled PCR conditions, the PCR-introduced error rate can be greatly minimized. This new procedure may be used to construct infectious chimeras of HIV or SIV for studies of vaccines and pathogenesis. Moreover, the method is designed to exchange viral genes at precise boundaries to study individual gene products from different HIV genomes. It can also be used to construct expression vectors for production of specific proteins or delivery vectors for gene transfer and gene therapy. Finally, the technique described here provides a versatile tool to transfer genes or gene fragments from different sources for genetic investigation and engineering.