Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

The secondary structure of oocyte and somatic 5S ribosomal RNAs of the fish Misgurnus fossilis L. from nuclease hydrolyses and chemical modification data.

We have studied the accessibility of 5'- 32P labeled oocyte and somatic 5S rRNAs from the fish Misgurnus fossilis L. to S1, T1 and cobra venom nucleases and have found that the cleavage sites of 5S rRNAs closely related in primary structures differ in these molecules. The data of nuclease hydrolyses revealed the existence of two conformers corresponding to renatured and partially denatured somatic 5S rRNA and capable of mutual interconversions. The exposed cytosine residues were located in oocyte and somatic 5S rRNAs converted into uridine ones by sodium bisulfite treatment. The data have been used to construct the secondary structure models of somatic and oocyte 5S rRNAs by means of specially devised computer program. These models differ in their 5'-halves which contain all the nucleotide substitutions in the primary structure, all differences in location of the exposed cytosine residues, and finally, in the cleavage pattern by the nucleases used.     

Secondary structure of the 5'-terminal region of the 18S ribosomal RNA5.3S fragment from the rat liver

Two small RNA fragments, 5,3S and 4,7S, were observed in gel electrophoretic analysis of RNA of the 40S ribosomal subunit of rat liver. 5,3S RNA (134-136 nucleotides long) proved to be 5'-terminal fragment of 18S ribosomal RNA, whereas 4,7 RNA is the degradation product of 5,3S RNA with 27-28 5'-terminal nucleotides lost. The secondary structure of 5,3S RNA was probed with two structure-specific nucleases, S1 nuclease and the double-strand specific cobra venom endoribonuclease. The nuclease digestion data agree well with the computer generated secondary structure model for 5,3S RNA. This model predicts that the 5'-terminal part of rat liver ribosomal 18S RNA forms an independent structural domain. The affinity chromatography experiments with the immobilized 5,3S fragment show that 5,3S RNA does not bind rat liver ribosomal proteins.     

Relocated interglacial lacustrine sediments from an esker at Snickarekullen, S.W. Sweden

Lumps of diatom-rich, laminated sediments were discovered redeposited and interbedded in a Late Weichselian delta sequence in a small glaciofluvial esker at Snickarekullen, south-western Sweden. Radiocarbon dating of the sediments gave an infinite age (45 000 B.P.). The composition and sediment structure of the lumps were studied in epoxy-impregnated thin sections using SEM and EDS. Quantitative and qualitative diatom analyses of the sediments were carried out, as well as pollen and macrofossils analyses. The biostratigraphy is compared with that from Holsteinian interglacial sites in surrounding countries, the evidence for which is briefly reviewed. It is concluded that the sediments were deposited in the central part of a lake probably during different parts of the Holsteinian interglacial. The water body changed from a rather shallow lake with a high pH to a considerably deeper, oligotrophic lake with neutral to slightly acidic water during the sedimentation period. The local and regional vegetation developed from an open pine-birch forest into a much more closed vegetation of pine, spruce, larch, alder and hornbeam.     

Two distinct conformations of rat liver ribosomal 5S RNA.

Three different conformers of rat liver 5S ribosomal RNA were investigated by partial nuclease cleavage technique using S1 nuclease and cobra venom endoribonuclease (CVE) as conformational probes. Urea-treated and renatured 5S RNA co-migrate on non-denaturing gels, but exhibit distinct differences in their nuclease cleavage patterns. The most prominent differences in S1 nuclease and CVE accessibility of these conformers are located in region 30-50 and around nucleotides 70 and 90. The third form of 5S RNA with higher electrophoretic mobility was generated by EDTA treatment. The cleavage patterns of this 5S RNA conformer are similar to that characteristic for the renatured 5S RNA. The results demonstrate the difference in secondary structure and possibly different tertiary base-pairing interactions of 5S RNA conformers.     

Location of single-stranded and double-stranded regions in rat liver ribosomal 5S RNA and 5.8S RNA.

Rat liver 5S rRNA and 5.8S rRNA were end-labelled with 32P at 5'-end or 3'-end of the polynucleotide chain and partially digested with single-strand specific S1 nuclease and double-strand specific endonuclease from the cobra Naja naja oxiana venom. The parallel use of these two structure-specific enzymes in combination with rapid sequencing technique allowed the exact localization of single-stranded and double-stranded regions in 5S RNA and 5.8 S RNA. The most accessible regions to S1 nuclease in 5S RNA are regions 33-42, 74-78, 102-103 and in 5.8 S RNA 16-20, 26-29, 34-36, 74-80 and a region around 125-130. The cobra venom endonuclease cleaves the following areas in 5S RNA: 7-8, 17-20, 28-30, 49-51, 56-57, 60-64, 69-70, 81-82, 95-97, 106-112. In 5.8S RNA the venom endonuclease cleavage sites are 4-7, 10-13, 21-22, 33-35, 43-45, 51-55, 72-74, 85-87, 98-99, 105-106, 114-115, 132-135. According to these results the tRNA binding sequences proposed by Nishikawa and Takemura [(1974) FEBS Lett. 40, 106-109], in 5S RNA are located in partly single-stranded region, but in 5.8S RNA in double-stranded region.