Stepwise assembly of a pre-mRNA splicing complex requires U-snRNPs and specific intron sequences

We have investigated the early events of pre-mRNA splicing in vitro by sucrose gradient sedimentation analysis. Time course experiments revealed the assembly, in two steps, of a large (50S) pre-mRNA splicing complex, preceded by formation of two other complexes that sediment at approximately 22S and 35S. Pre-mRNA and the intermediates and products of the in vitro splicing reaction cosediment with the 50S complex, while only pre-mRNA is associated with the 22S and 35S complexes. No splicing is observed in the absence of a 50S complex. Formation of the 50S complex requires ATP, whereas formation of the 22S and 35S complexes does not. U-snRNPs are necessary for assembly of the 35S and the 50S complexes but not for assembly of the 22S complex. Analysis with mutant substrate RNAs demonstrated that a polypyrimidine stretch near the 3' splice site and an intact 5' splice site are absolutely required for splicing complex formation.     

Isolation and characterization of Pediococcus halophilus from salted anchovies (Engraulis anchoita)

The presence of bacteria in salted anchovies during and at the end of the curing process was investigated. Attempts to isolate bacteria under aerobic or anaerobic conditions led to the isolation of only bacteria of the genus Pediococcus which were identified as Pediococcus halophilus. The isolates correspond to a rather heterogeneous group in which some of the members differ in some biochemical tests from the types described in the literature.     

Analysis of an activatable promoter: sequences in the simian virus 40 late promoter required for T-antigen-mediated trans activation.

The late promoter of simian virus 40 (SV40) is activated in trans by the viral early gene product, T antigen. We inserted the wild-type late-promoter region, and deletion mutants of it, into chloramphenicol acetyltransferase transient expression vectors to identify promoter sequences which are active in the presence of T antigen. We defined two promoter activities. One activity was mediated by a promoter element within simian virus 40 nucleotides 200 to 270. The activity of this element was detectable only in the presence of an intact, functioning origin of replication and accounted for 25 to 35% of the wild-type late-promoter activity in the presence of T antigen. The other activity was mediated by an element located within a 33-base-pair sequence (simian virus nucleotides 168 to 200) which spans the junction of the 72-base-pair repeats. This element functioned in the absence of both the origin of replication and the T-antigen-binding sites and appeared to be responsible for trans-activated gene expression. When inserted into an essentially promoterless plasmid, the 33-base-pair element functioned in an orientation-dependent manner. Under wild-type conditions in the presence of T antigen, the activity of this element accounted for 65 to 75% of the late-promoter activity. The roles of the 33-base-pair element and T antigen in trans-activation are discussed.     

Are Chaoborus larvae more abundant in acidified than in non-acidified lakes in Central Canada?

Eriksson et al (1980) hypothesized that the abundance of certain macroinvertebrate predators, such as larvae of the phantom midge Chaoborus , should increase in acidified lakes because of the elimination of fish. To examine the influence of pH and presence of fish on Chaoborus abundance, we surveyed Chaoborus populations in 33 lakes in Ontario, Canada which ranged in pH from 4.5 to 7.4. Chaoborus larvae were not more abundant in the acidified lakes that were devoid of fish than in the remaining lakes. Therefore, we concluded that pH and presence of fish are not prime determinants of total Chaoborus abundance in Canadian Shield lakes. We hypothesized that significant increases in Chaoborus abundance should only be anticipated when fish populations are eliminated by acidification of relatively nutrient rich lakes.     

Variants within the yeast Ty sequence family encode a class of structurally conserved proteins.

The Ty transposable elements of Saccharomyces cerevisiae form a heterogeneous family within which two broad structural classes (I and II) exist. The two classes differ by two large substitutions and many restriction sites. We show that, like class I elements a class II element, Tyl-17, also appears to contain at least two major protein coding regions, designated TYA and TYB, and the organisational relationship of these regions has been conserved. The TYA genes of both classes encode proteins, designated p1 proteins, with an approximate molecular weight of 50 Kd and, despite considerable variation between the TYA regions at the DNA level, the structures of these proteins are remarkably similar. These observations strongly suggest that the p1 proteins of Ty elements are functionally significant and that they have been subject to selection.     

Nucleotide sequence characterization of Ty 1-17, a class II transposon from yeast

We have determined the nucleotide sequence of a class II yeast transposon (Ty 1-17) which is found just centromere-distal to the LEU2 structural gene on chromosome III of Saccharomyces cerevisiae. The complete element is 5961 bp long and is bounded by two identical, directly repeated, delta sequences of 332 bp each. The sequence organization indicates that Ty 1-17 is a retrotransposon, like the class I elements characterized previously. It contains two long open reading-frames, TyA (439 amino acids) and TyB (1349 amino acids). In this paper, the sequences of the two classes of yeast transposon are compared with one another and with analogous elements, such as retroviral proviruses, cauliflower mosaic virus and copia sequences. Features of the Ty 1-17 sequence which may be important to its mechanism of transposition and its genetic action are discussed.     

β-D-galactosidase ofLactobacillus species

The activity of β-D-galactosidase was studied in 13 strains of lactobacilli (groupsStreptobacterium, Thermobacterium andBetabacterium). Using 2-nitrophenyl galactopyranoside as substrate, the enzyme activity varied with the strain. The values found in theThermobacterium group were superior to those in theStreptobacterium group. The optimum pH for the species belonging to theThermobacterium group was uniform, in contrast to the ph for those from theStreptobacterium which varied according to the species. The optimum temperature was quite uniform within each group and higher in theStreptobacterium. Lactose acted as a competitive inhibitor. MgCl₂ protected the enzyme from thermal denaturation. The calcium ions inhibited the activity in all cases. The behaviour of the protectors of the SH groups varied according to the strain. 6-Phospho-β-D-galactosidase activity was also determined, levels lower than β-D-galactosidase were found, except inLactobacillus plantarum ATCC 8014 and 14917.     

The influence of a fall fumigation with ozone on the stomatal behavior of spruce and fir

Summary Clonal stock (grafts of 15-, 50-, and 100-year-old trees) of spruce (Picea abies (L.) Karst.) and fir (Abies alba Mill.) was exposed either to 150 ppb ozone (300 gm^-3) during 9 daylight hours or to carbon-filtered air on 35 days between 29 August and 21 October 1983. At the end of the fumigation the trees did not exhibit any visible signs of injury. Transpiration and leaf conductance in light and darkness, measured with a Licor porometer, revealed, however, stomatal sluggishness and — in spruce-increased transpiration.