Identification of three different plasmid-encoded restriction/modification systems in Streptococcus lactis subsp. cremoris W56

Abstract Streptococcus lactis subsp. cremoris W56 ( S. cremoris W56) is a strain partially resistant to phage attack. Derivatives which had lost either plasmid pJW563 or pJW566 no longer expressed the restriction and modification systems encoded by these plasmids. Genetic evidence for the correlation between the plasmids and the R/M systems was obtained by transformation. In addition, a third R/M system was discovered among the transformants and was shown to be encoded by pJW565. Thus, genetic evidence for at least 3 distinct R/M systems encoded by plasmids in S. cremoris W56 is presented. One of the R/M-systems showed stronger restriction of the isometric phage p2 than of the prolate phage c2. The other two systems restricted both classes of phages with equal efficiencies.     

Purification of recombinant proteins by immunoaffinity chromatography with preselected antibodies

Summary Nuclease produced by recombinant Escherichia coli was successfully purified by immunoaffinity chromatography using an antibody preselected for the purpose on the basis of an elution assay. The elution assay was also used to optimize elution conditions. One step recovery of nuclease from crude periplasmic extract was 66%.