IDENTIFICATION AND CHARACTERIZATION OF IS1381, A NEW INSERTION-SEQUENCE IN STREPTOCOCCUS-PNEUMONIAE

A new insertion sequence (IS1381) was identified in the genome of Stre ptococcus pneumoniae R6 as an 846-bp segment containing 20-bp terminal inverted repeats and flanked by 7-bp direct repeats. The three sequen ced copies of this element have two overlapping open reading frame (OR F) genes named orfA and orfB. However, significant variations between individual copies were found, suggesting that inactivating mutations h ave occurred in an original single ORF. Accordingly, the consensus IS1 381 element derived from the comparison of the three available copies should contain a single ORF sufficient to encode a basic protein of 26 7 amino acids which exhibited high similarity to the putative transpos ases of ISL2 from Lactobacillus helveticus add of IS702 from the cyano bacterium Calothrix sp, strain PCC 7601. A minimum of five to seven co pies were detected by hybridization experiments in the R6 genome. In r emarkable contrast with the two previously reported pneumococcal inser tion sequences, several copies of IS1381 have been detected in all of the clinical isolates tested so far. Interestingly, Streptococcus oral is NCTC 11427 (type strain), a close relative of pneumococcus, does ho t contain this element, but its occurrence in the type strain of Strep tococcus mitis (NCTC 12261) suggests that this species hs exchanged DN A with S. pneumoniae directly or through an intermediate species.