[Primary structure of the 5.8S gene of rRNA and internal transcribed spacers of rDNA in diploid wheat Triticum urartu thum. ex. gandil]

Nucleotide sequences of 5.8S rRNA gene and rDNA internal transcribed spacers ITS-1 and ITS-2 were determined in diploid wheat Triticum urartu. It was shown that 5.8S rRNA gene of this wheat species consists of 163 base pairs and GC-content is 59.5%. When comparing 5.8S rRNA sequences in diploid wheat, rice and lupine and also 5.8S rRNA in hexaploid wheat and horse beans a high evolutional conservatism of its structure was revealed. The size of ITS-1 and ITS-2 in Tr. urartu is 219 and 225 base pairs long correspondingly. While comparing structures of similar rDNA regions of Tr. urartu, rice and maize a high level of homology was found only between nucleotides adjoining genes of high molecular rRNAs. In ITS-1 of Tr. urartu an insertion of 5'-GACGACGACATTGTCCGTC-3' was found, which is absent in maize and rice.

Organization of ribosomal RNA genes in the fungus Cochliobolus heterostrophus

The genes encoding the 17S, 5.8S and 25S ribosomal RNAs in the Ascomycete Cochliobolus heterostrophus were cloned and analyzed. They are arranged in tandemly repeated units (rDNA) either 9.0 or 9.15 kilobases in length, depending upon the strain. The 5S rRNA genes are not part of the tandemly repeated rDNA. Instead, many and perhaps all of the 5S genes are dispersed in the genome, as they are in the fungi Neurospora, Aspergillus and Schizosaccharomyces. Comparative restriction maps of the rDNA from C. heterostrophus and other filamentous fungi and yeasts are presented. A survey of rDNAs from twenty-three field isolates of C. heterostrophus collected worldwide demonstrated that each isolate has one or the other of two rDNA forms, which differ in length and in the presence or absence of at least three restriction enzyme sites. The differences are all located in spacer DNA outside the coding regions for the rRNA genes. Heterogeneity in the rDNA repeat was not observed within any single isolate. The copy number of the rRNA gene cluster in C. heterostrophus is approximately 130 per haploid genome.

Ribosomal gene structure, variation and inheritance in maize and its ancestors

We have examined the structure of nuclear genes coding for ribosomal RNAs in maize and its wild relatives, the teosintes and Tripsacum. Digestion of the rDNA (genes coding for 18S, 5.8S and 26S RNAs) with 15 restriction endonucleases (with six base pair recognition sites) yields essentially a single map for the approximately 10,000 repeat units within an individual plant or species. Both length and site variation were detected among species and were concentrated in the intergenic spacer region of the rDNA repeat unit. This result is in agreement with patterns of rDNA change observed among wheat and its relatives (Triticeae), and among vertebrate species. Digestion of these nuclear DNAs with BamHI and subsequent hybridization with a 5S RNA gene-specific probe allowed determination of the size of the 5S gene repeat unit in maize, teosintes, and Tripsacum. Groupings in the genus Zea were characterized by distinct repeat unit types five Tripsacum species examined shared a 260 base pair major repeat unit type. Additionally, several other restriction endonuclease cleavage patterns differentiated among the 5S DNAs within the genus Zea. The rDNA and 5S DNA restriction site variation among the species can be interpreted phylogenetically and agrees with biochemical, karyotypic, and morphological evidence that places maize closest to the Mexican teosintes. For both gene arrays, contributions from each parental genome can be detected by restriction enzyme analysis of progeny from crosses between maize and two distantly related teosintes, Zea luxurians or Zea diploperennis, but certain teosinte arrays were underrepresented in some of the hybrids.

Unusual ribosomal RNA of the intestinal parasite Giardia lamblia

The anaerobic protozoan Giardia lamblia is a common intestinal parasite in humans, but is poorly defined at molecular and phylogenetic levels. We report here a structural characterization of the ribosomal RNA (rRNA) and rRNA genes of G. lamblia. Gel electrophoresis under native or non-denaturing conditions identified two high molecular weight rRNA species corresponding to the 16-18S and 23-28S rRNAs. Surprisingly, both species (1300 and 2300 nucleotides long, respectively) were considerably shorter than their counterparts from other protozoa (typically 1800 and 3400 nucleotides), and from bacteria as well (typically 1540 and 2900 nucleotides long). Denaturing polyacrylamide gel electrophoresis identified a major low molecular RNA of 127 nucleotides and several minor species, but no molecules with the typical lengths of 5.8S (160 nucleotides) and 5S (120 nucleotides) rRNA. The G. lamblia 1300, 2300, and 127 nucleotide RNAs are encoded within a 5.6 kilobase pair tandemly repeated DNA, as shown by Southern blot analysis and DNA cloning. Thus, the rRNA operon of this eukaryotic organism can be no longer than a typical bacterial operon. Sequence analysis identified the 127 nucleotide RNA as homologous to 5.8S RNA, but comparisons to archaebacterial rRNA suggest that Giardia derived from an early branch in eukaryotic evolution.