A transposon-like element on the lactose plasmid of Lactococcus lactis subsp. lactis Z270

An inverted repeat previously called IR was identified on the lactose plasmid of Lactococcus lactis subsp. lactis Z270 by self-annealing; it was now named IS1076. The two sequences were 3.3 kb apart. Both copies were cloned in E. coli, sequenced and found to be identical, except for an additional 44 bp direct repeat at the 5' end of the right-hand copy; they were thus respectively 1296 bp (IS1076R) and 1252 bp (IS1076L) long. Both elements end in near-perfect 39 bp inverted repeats, similar to the IS904 termini. Promoter consensus sequences and a RBS site precede an ORF1 of 384 amino acids. Subclones of IS1076R and IS1076L produced a new 44 kDa protein corresponding to the size of the ORF1. The distal part of the ORF1 coding region is very similar to the IS3 ORFI sequence and the IS904 ORF sequence, and the proximal part shows some homologies with IS3 ORFII. A three-base target is present as a direct repeat flanking the 5.9 kb genetic block including IS1076L, IS1076R and the internal region, resulting in a structure similar of that of a transposon.