A GROUP-I INTRON IN THE TERMINASE GENE OF LACTOBACILLUS-DELBRUECKII SUBSP LACTIS PHAGE LL-H

An 837 nt long group IA intron was discovered in the Lactobacillus del brueckii subsp. lactis virulent phage LL-H genome. The LL-H intron con forms well to the secondary structure that is common to all group I in trons. The only exception is that the extreme 3' nucleotide of the int ron is an A residue instead of the usual G; despite this the intron is efficiently spliced in vivo. This LL-H intron contains an ORF, ORF168 , which shows homology with endonucleases encoded by ORFs contained in Bacillus subtilis phage introns. At present, the LL-H intron is the o nly one found in the phages of lactic acid bacteria and the first one to be found in a phage belonging to the most abundant taxonomic group, group B or Siphoviridae. The LL-H intron interrupts gene terL, the pr oduct of which (50.5 kDa, TerL) is significantly homologous to the lar ge subunit of B. subtilis phage SPP1 terminase. The product of the ups tream gene, terS of LL-H (15.9 kDa, TerS), shows homology to small sub units of B. subtilis phage terminases.