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, Hin dIII, 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'-terminat ed single strands protruding from both ends. The nucleotide sequence o f the cohesive ends, determined by the dideoxynucleotide method, compr ised four A+T and 10 G+C pairs: 5' GAGGCCGACCGTTC3'/3'CTCCGGCTGGCAAG 5 '. Thus, the cohesive ends of PL-1 DNA were higher in G+C content than those of other known bacteriophage DNAs.