COMPARATIVE-ANALYSIS OF THE GENOMIC DNA TERMINAL REGIONS OF THE LACTOCOCCAL BACTERIOPHAGES FROM SPECIES C2

In an attempt to compare the cos intergenic region and bordering ORFs from Lactococcus lactis bacteriophages of the species c2, the nucleoti de sequence of a 2479-bp fragment containing the cos site of phage P00 1 DNA was determined and compared with the corresponding regions of ph ages c2, bIL67 and P6 (partial sequence), which belong to species c2. This comparative analysis revealed that some characteristic features o f the cos intergenic region are conserved in all members of species c2 . Some of them are specific to species c2, as is the case for a GC-ric h repeat in phase with the double helix that is located dose to cos. O ne conserved motif seems to be more general, as it is found in all the cos regions of L. lactis bacteriophages that have been sequenced. It consists in a 4-nt indirect repeat TCAN/NACT located in a 15-bp fragme nt containing cos. This motif may be related to terminase specificity, as most of the cos asymmetric cleavages identified up to now are loca ted within, or at the border of,these indirectly repeated sequences. F inally, some of the conserved DNA motifs of the species c2 cos-interge nic region seem to be even more general, as they are homologous to the lambda-R sites known to be involved in the maturation and the encapsi dation of phage lambda DNA. Our comparative analysis also showed that within c2 phage DNAs, large blocks of sequences, i.e. the intergenic c os region and ORF/17 on the one hand, and ORF/16 on the other hand, ev olved as distinct entities, probably by block recombination between ph age DNAs of the same species.