E. coli extract assays of retrohoming in wild-type and mutant strains.

Values were determined by measuring the amount of radioactivity in the indicated product band or bands relative to that in the substrate band after subtraction of background and are expressed relative to the corresponding values for the parental wild-type strain assayed in parallel. Total reverse splicing was quantified by measuring the radioactivity in all bands larger than the DNA substrate band in reactions with top-strand labeled DNA substrate without RNase treatment of the products. Total cDNA was quantified by measuring the radioactivity in all bands larger than the DNA substrate band in reactions with bottom-strand labeled DNA substrate after RNase treatment of the products. Full-length bottom strand was quantified by measuring the radioactivity in the band corresponding to the full-length bottom-strand product (988 nt) in reactions with 5′ bottom-strand labeled DNA substrate after RNase treatment of the products. Full-length top strand was quantified by measuring the radioactivity in the band corresponding to the full-length top-strand product (988 nt) after RNase treatment of the products. Radioactivity was determined by scanning the dried gel with a Typhoon Trio PhosphorImager and quantifying using ImageQuant TL.aC0719 is a transposon-insertion mutant in the HMS174(DE3) strain background.bThe lexA mutant is lexA51::Tn5 in the SS996 strain background and has a constitutively induced SOS response [60].cThe pnp mutant is the pnp-7 allele in the PR100 strain background and has [88].dThe ΔpriB mutation is a complete deletion of the gene in the SS996 strain background; the priB deletion strain sent by the Keio collection was found to retain the gene.