RIBOSOMAL-RNA GENE ORGANIZATION IN CRYPTOSPORIDIUM-PARVUM

The cytoplasmic ribosomal RNA (rRNA) genes of the Apicomplexan protozo an parasite Cryptosporidium parvum have been analyzed with respect to size, copy number, organization and structure. The small and large sub unit rRNAs are 1.7 and 3.6 kb, respectively. A 151 bp putative 5.8S rR NA gene was identified. The rDNA unit is 5' small subunit rRNA-interna l transcribed spacer 1-5.8S rRNA-internal transcribed spacer 2-large s ubunit rRNA 3'. There are five copies of the rDNA unit per haploid gen ome and they are not organized in a conventional head to tail tandem a rray with a conserved external transcribed spacer. The rDNA units are dispersed through the genome to at least three chromosomes. At least t wo of the rDNA units are single unlinked copies on different chromosom es. There are two structurally distinct types of rDNA unit, Type A and B, with marked differences in the internal transcribed spacer regions . There are four copies of the Type A rDNA unit and one copy of the Ty pe B rDNA unit. (C) 1997 Elsevier Science B.V.