FIG. 1.

Intron region and the splicing-dependent conjugation assay. (a) Map of the intron region of pRS01 (not to scale). As described by Mills et al. (18), the ltr genes are involved in transfer of pRS01. ltrF has not been described previously, but it is predicted to encode a protein translated from the UUG alternative start codon. The bar under the map indicates the location of the pRS01 origin of transfer (oriT). Intron Ll.ltrB disrupts the ltrBE1 and ltrBE2 exons and encodes the ltrA gene. A bent arrow indicates the ltrA promoter internal to the intron. The arrows under the map indicate the positions of primers RTPCRltrBE1 and RTltrBE2 used in the RT-PCR splicing assay. A portion of the transfer region is carried by the shuttle vector pCOM9, as indicated by the line below the map. (b) Schematic diagram of the conjugation-based genetic assay for splicing. Splicing of Ll.ltrB from pCOM9 allows production of functional LtrB protein. LtrB protein acts in trans to nick pM1014 oriT and promote pM1014 transfer to the recipient cell.