title: Restriction endonuclease analysis of the lactose plasmid in Streptococcus lactis ML3 and two recombinant lactose plasmids.
abstract: We investigated the molecular relationship between the 60-megadalton (Mdal) recombinant lactose plasmids in ML 3 x LM2301 lactose-positive (Lac+) transconjugants and the genetic material of Streptococcus lactis ML3. Lactose metabolism is linked to the 33-Mdal plasmid pSK08 in ML3, and the recipient LM2301 is cured of plasmid DNA. The plasmids were analyzed with a series of restriction enzymes. We found that the 60-Mdal plasmids of Lac+ transconjugants contained pSK08 DNA, but were not simply dimers of pSK08. The 60-Mdal plasmids contained a segment of DNA not apparent in pSK08. The restriction patterns of the 60-Mdal plasmid in a Lac+ nonclumping transconjugant and that in a Lac+ clumping transconjugant were different. This suggested that there was a molecular differences between these two recombinant plasmids. We conclude that the segment of DNA in the 60-Mdal plasmids that was not present in pSK08 was the proposed transfer factor responsible for cell aggregation and high-frequency conjugation.
mesh_terms: D001483:Base Sequence; D003227:Conjugation, Genetic; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D010957:Plasmids; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D004262:DNA Restriction Enzymes; D007785:Lactose