The genes for 5 S ribosomal RNA and transfer RNA in Tetrahymena pyriformis.

In the present communication a characterization of the 5 S rRNA genes and the tRNA genes of Tetrahymena pyriformis has been performed. The number of 5 S rRNA and tRNA genes in the macromolecular DNA has been established. Furthermore no sequence homology is observed for these genes. The number of both types of genes does not change significantly under starvation conditions. The genomic organization of the 5 S rRNA and tRNA genes has been investigated. From in vivo replication studies it is concluded, that replication of both 5 S rRNA and tRNA genes takes place throughout the whole S-period.     

Nucleocytoplasmic transport of 5S ribosomal RNA

Nucleocytoplasmic transport of 5S ribosomal RNA in Xenopus oocytes occurs in the context of small, non-ribosomal RNPs. The complex with the zinc finger protein TFIIIA (7S RNP) is exported from the nucleus and stored in the cytoplasm, whereas the complex with the ribosomal protein L5 (5S RNP) shuttles between the nucleus and the cytoplasm. Nuclear import- and export-signals appear to reside within the protein moiety of these RNPs. Import of TFIIIA is inhibited by RNA binding, whereas nuclear transfer of L5 is not influenced by RNA binding. We propose that the export capacity of both, TFIIIA and L5, is regulated by the interaction with 5S ribosomal RNA.     

Oocyte and somatic 5S ribosomal RNA and 5S RNA encoding genes in Xenopus tropicalis.

We have investigated the structure of oocyte and somatic 5S ribosomal RNA and of 5S RNA encoding genes in Xenopus tropicalis. The sequences of the two 5S RNA families differ in four positions, but only one of these substitutions, a C to U transition in position 79 within the internal control region of the corresponding 5S RNA encoding genes, is a distinguishing characteristic of all Xenopus somatic and oocyte 5S RNAs characterized to date, including those from Xenopus laevis and Xenopus borealis. 5S RNA genes in Xenopus tropicalis are organized in clusters of multiple repeats of a 264 base pair unit; the structural and functional organization of the Xenopus tropicalis oocyte 5S gene is similar to the somatic but distinct from the oocyte 5S DNA in Xenopus laevis and Xenopus borealis. A comparative sequence analysis reveals the presence of a strictly conserved pentamer motif AAAGT in the 5'-flanking region of Xenopus 5S genes which we demonstrate in a separate communication to serve as a binding signal for an upstream stimulatory factor.     

Precursors of 5 S ribosomal RNA in Bacillus subtilis

Bacillus subtilis 168 accumulates subnormal quantities of mature 5 S ribo-somal RNA in the presence of inhibitors of protein synthesis, such as chloramphenicol, or during pulse-labeling experiments. However, two RNA species, evidently precursors of m5 rRNA and therefore designated as p5_A and p5_B, do accumulate under these conditions. These RNA species are substantially longer than B. subtilis m5 rRNA: p5_A is about 179 nucleotides in length and p5_B is composed of approximately 152 nucleotides. The sum of p5_A, p5_B and m5 rRNA accumulating in the absence of protein synthesis, less excess chain length associated with p5_A and p5_B, equals the expected quantities of m5 rRNA in growing cells. p5_A and p5P_B both contain all t₁ RNase-generated oligonucleotides characteristic of m5 rRNA plus additional sequences. At least the 5′ termini of p5_A and p5_B differ from that of m5. If chloramphenicol is removed from a culture in which p5_A and p5_B have accumulated and further RNA synthesis is inhibited, then a quantitative reciprocal loss of p5_A and p5_B occurs as m5 rRNA accumulates. No evidence suggests any p5_A to p5_B transition under these conditions.     

5 S and 5.8 S ribosomal RNA sequences and protist phylogenetics

More than 100 5 S 5.8 S rRNA sequences from protists, including fungi, are known. Through a combination of quantitative treeing and special consideration of "signature' nucleotide combinations, the most significant phylogenetic implications of these data are emphasized. Also, limitations of the data for phylogenetic inferences are discussed and other significant data are brought to bear on the inferences obtained. 5 S sequences from red algae are seen as the most isolated among eukaryotics. A 5 S sequence lineage consisting of oomycetes, euglenoids, most protozoa, most slime molds and perhaps dinoflagellates and mesozoa is defined. Such a lineage is not evident from 5.8 S rRNA or cytochrome c sequence data. 5 S sequences from Ascomycota and Basidiomycota are consistent with the proposal that each is derived from a mycelial form with a haploid yeast phase and simple septal pores, probably most resembling present Taphrinales. 5 S sequences from Chytridiomycota and Zygomycota are not clearly distinct from each other and suggest that a major lineage radiation occurred in the early history of each. Qualitative biochemical data clearly supports a dichotomy between an Ascomycota-Basidiomycota lineage and a Zygomycota-Chytridiomycota lineage.     

Effect of blue and red light on the synthesis of ribosomal RNA in Chlorella]

In autotrophic cultures of Chlorella pyrenoidosa (strain 211-8b) incorporation of tritiated guanosine and uridine into ribosomal RNA is stimulated by light. Blue light of wavelengths around 457 nm is considerably more effective than red light around 679 nm (5-10(-10) Einstein cm-2 sec-1 for both). This effect can be demonstrated for young daughter cells (at the end of the dark period) and for older cells (at the end of the light period). It is shown to depend on a regulation of rRNA-synthesis. The blue light dependent enhancement of incorporation is more pronounced in the cytoplasmic rRNA (25 and 18 s) than in the chloroplast rRNA (23 and 16 s). Blue light of low intensity (1-10(-10) Einstein cm-2 sec-1) has nearly the same effectivity as the fivefold intensity, whereas red light of equal quantum fluxes enhances incorporation only slightly compared with the dark control. The blue light dependent enhancement of rRNA-synthesis continues in the following darkness in contrary to that caused by red light. This enhancement is also found in DCMU-poisened cultures. In contrast to this, is red light in presence of DCMU, incorporation into rRNA is nearly the same as in dark. It is concluded that the regulation of rRNA-synthesis in red light is closely connected to complete photosynthesis, while in blue light an additional regulation takes place independent of photosynthesis.     

5S ribosomal RNA is contained within a 25 S ribosomal RNA that accumulates in mutants of Escherichia coli defective in processing of ribosomal RNA.

A temperature-sensitive mutant strain of Escherichia coli defective in two RNA processing enzymes, RNase III and RNase E (rnc. rne), fails to produce normal levels of 23 S and 5 S rRNA at the non-permissive temperature. Instead, a molecule larger than 23 S is produced. This molecule, designated 25 S rRNA, can be processed in vitro to produce p5 rRNA. These findings further our understanding of the overall processing events of ribosomal RNA which take place in the bacterial cell.