Cloning and sequencing of a 16S/23S ribosomal spacer from Haemophilus parainfluenzae reveals an invariant, mosaic-like organisation of sequence blocks

A 16S/23S ribosomal spacer from a Haemophilus parainfluenzae rrn locus was cloned and sequenced. Analysis of PCR-amplified genomic fragments showed that this region is strongly conserved among unrelated isolates; computer analysis of database homologies showed that the spacer consists of sequence blocks, arranged in a mosaic-like structure, with strong homologies with analogous blocks present in the spacer regions of Haemophilus influenzae, Haemophilus ducreyi andActinobacillus spp. It also contains a tRNAqlu gene, which is highly homologous to tRNAqlu genes found in spacers of other species. These data strongly support the hypothesis that recombination events are involved in the organisation of the sequence of the spacer, as a result of horizontal gene transfer.