Restriction map of the genomic DNA of Lactobacillus casei bacteriophage PL-1 and nucleotide sequence of its cohesive single-stranded ends.

A restriction map of the genomic DNA of Lactobacillus casei phage PL-1 was constructed using the restriction endonucleases BamHI, EcoRI, HindIII, KpnI, NruI and XhoI. The PL-1 genome was 42.2 kb in size and had complementary cohesive ends forming a ring-like monomer. The cohesive ends, analysed with exonuclease III and S1 nuclease, were 3'-terminated single strands protruding from both ends. The nucleotide sequence of the cohesive ends, determined by the dideoxynucleotide method, comprised four A + T and 10 G + C pairs: 5' GAGGCCGACCGTTC 3'/3' CTCCGGCTGGCAAG 5'. Thus, the cohesive ends of PL-1 DNA were higher in G + C content than those of other known bacteriophage DNAs.