A NEW RDNA REPEAT UNIT IN HUMAN GIARDIA

The rDNA repeat unit from a new human Giardia duodenalis strain shows significant differences from the previously reported G. duodenalis rDN A repeat. Twelve base-pair changes occurred in 490 bp of the SSrRNA ge ne and new restriction enzyme sites occurred in the LSrRNA gene. The o verall length of the rRNA genes is the same but the spacer is 76 bp lo nger than previously reported. A boundary within the spacers of the tw o different rDNA units divides a region of 50% homology near the LSrRN A gene from a region of 80% homology toward the SSrRNA gene. This boun dary region includes two copies of a 78 bp repeat.