A host factor absent from Lactococcus lactis subspecies lactis MG1363 is required for conjugative transposition.
In matings between Lactococcus lactis strains, the conjugative transposons Tn916 and Tn919 are found in the chromosome of the transconjugants in the same place as in the chromosome of the donor, indicating that no transposition has occurred. In agreement with this, the frequency of L. lactis transconjugants from intraspecies matings is the same whether the donor contains the wild-type form of the transposon or the mutant Tn916-int1, which has an insertion in the transposon's integrase gene. However, in intergeneric crosses with Bacillus subtilis or Enterococcus faecalis donors, Tn916 and Tn919 transpose to different locations on the chromosome of the L. lactis transconjugants. Moreover, Tn916 and Tn919 could not be transferred by conjugation from L. lactis and B. subtilis, E. faecalis or Streptococcus pyogenes. This suggests that excision of these elements does not occur in L. lactis. When cloned into E. coli with adjacent chromosomal DNA from L. lactis, the conjugative transposons were able to excise, transpose and promote conjugation. Therefore, the inability of these elements to excise in L. lactis is not caused by a permanent structural alteration in the transposon. We conclude that L. lactis lacks a factor required for excision of conjugative transposons.
Bringel
F
F
Department of Microbiology and Immunology, Emory University Health Sciences Center, Atlanta, Georgia 30322.
Van Alstine
G L
GL
Scott
J R
JR
D001412:Bacillus subtilis / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics*; D003227:Conjugation, Genetic; D003433:Crosses, Genetic; D004254:DNA Nucleotidyltransferases / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D013293:Enterococcus faecalis / Q000235:genetics; D029968:Escherichia coli Proteins; D019426:Integrases; D034982:Integration Host Factors; D013294:Lactococcus lactis / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D013297:Streptococcus pyogenes / Q000235:genetics
D002352:Carrier Proteins; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D034982:Integration Host Factors; C440502:integration host factor, E coli; D004254:DNA Nucleotidyltransferases; D019426:Integrases