Artificial nondirectional site-specific recombination systems.
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ABSTRACT:
SUBMITTER: Wang JY
PROVIDER: S-EPMC8762395 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Site-specific recombinases have become a resourceful tool for genome engineering, allowing sophisticated in vivo DNA modifications and rearrangements, including the precise removal of integrated retroviruses from host genomes. In a recent study, a mutant form of Cre recombinase has been used to excise the provirus of a specific HIV-1 strain from the human genome. To achieve provirus excision, the Cre recombinase had to be evolved to recombine an asymmetric locus of recombination (lox)-like sequence present in the long terminal repeat (LTR) regions of a HIV-1 strain. One pre-requisite for this type of work is the identification of degenerate lox-like sites in genomic sequences. Given their nature-two inverted repeats flanking a spacer of variable length-existing search tools like BLAST or RepeatMasker perform poorly. To address this lack of available algorithms, we have developed the web-server SeLOX, which can identify degenerate lox-like sites within genomic sequences. SeLOX calculates a position weight matrix based on lox-like sequences, which is used to search genomic sequences. For computational efficiency, we transform sequences into binary space, which allows us to use a bit-wise AND Boolean operator for comparisons. Next to finding lox-like sites for Cre type recombinases in HIV LTR sequences, we have used SeLOX to identify lox-like sites in HIV LTRs for six yeast recombinases. We finally demonstrate the general usefulness of SeLOX in identifying lox-like sequences in large genomes by searching Cre type recombination sites in the entire human genome. SeLOX is freely available at http://selox.mpi-cbg.de/cgi-bin/selox/index.
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Project description:Phage-encoded serine integrases mediate directionally regulated site-specific recombination between short attP and attB DNA sites without host factor requirements. These features make them attractive for genome engineering and synthetic genetics, although the basis for DNA site selection is poorly understood. Here we show that attP selection is determined through multiple proofreading steps that reject non-attP substrates, and that discrimination of attP and attB involves two critical site features: the outermost 5-6 base pairs of attP that are required for Int binding and recombination but antagonize attB function, and the "discriminators" at positions -15/+15 that determine attB identity but also antagonize attP function. Thus, although the attachment sites differ in length and sequence, only two base changes are needed to convert attP to attL, and just two more from attL to attB. The opposing effect of site identifiers ensures that site schizophrenia with dual identities does not occur.
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