Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat

The ribosomal RNA (rRNA) genes of Giardia lamblia are organized in tandem arrays of a 5.6 kb repeat (1, 2). Genomic DNA digested with the restriction endonuclease Xbal, which does not cut within the rRNA repeat, showed a fuzzy rRNA hybridizing band of 6.5 to 7.5 kb (Figure 1A). We examined the potential telomeric location of these rRNA-containing fragments by digesting genomic DNA with BAL 31 followed by digestion with Xbal (Figure 1A). BAL 31 digestion resulted in the disappearance of the 7 kb smear and the appearance of a homogeneous band that was progressively shortened (15 bp/min). A band at 10 kb also showed BAL 31 sensitivity. The high molecular weight DNA encoding rRNA genes readily distributes into a smear upon continued BAL 31 digestion, indicative of other telomerically located rRNA genes (3). Shortening of fragments hybridizing with a /3-tubulin contro