Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review

A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed.     

Differential regulation of the accumulation of the light-harvesting chlorophyll a/b complex and ribulose bisphosphate carboxylase/oxygenase in greening pea leaves

The photoregulation of chloroplast development in pea leaves has been studied by reference to three polypeptides and their mRNAs. The polypeptides were the large subunit (LSU) and the small subunit (SSU) of ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO), and the light-harvesting chlorophyll a/b protein (LHCP). The polypeptides were assayed by a sensitive radioimmune assay, and the mRNAs were assayed by hybridization to cloned DNA probes. LSU, LSU mRNA, and LHCP mRNA were detectable in etiolated seedlings but LHCP, SSU, and SSU mRNA were at or below the limit of detection. During the first 48 hr of de-etiolation under continuous white light, the mRNAs for LSU, SSU, and LHCP increased in concentration per apical bud by about 40-fold, at least 200-fold, and about 25-fold, respectively, while the total RNA content per apical bud increased only 3.5-fold. In the same period, the LSU, SSU, and LHCP contents per bud increased at least 60-, 100-, and 200-fold, respectively. The LHCP increased steadily in concentration during de-etiolation, whereas the accumulation LSU, SSU, and SSU mRNA showed a 24-hr lag. The accumulation of SSU, SSU mRNA, and LHCP mRNA showed classical red/far-red reversibility, indicating the involvement of phytochrome in the regulatory mechanism. LSU and LSU mRNA were induced equally well by red and far-red light. The LHCP failed to accumulate except under continuous illumination. These results indicate that the accumulation of SSU is controlled largely through the steady-state level of its mRNA, which is in turn almost totally dependent on light as an inducer and on phytochrome as one of the photoreceptors. The accumulation of LSU is largely but not totally determined by the level of its mRNA, which appears to be under strong photoregulation, which has yet to be shown to involve phytochrome. Phytochrome is involved in the regulation of LHCP mRNA levels but substantial levels of the mRNA also occur in the dark. LHCP accumulation is not primarily governed by the levels of LHCP mRNA but by posttranslational stabilization in which chlorophyll synthesis plays a necessary but not sufficient role.     

STUDIES ON THE AUTECOLOGY OF THE MARINE DIATOM THALASSIOSIRA NORDENSKIOELDII. II. THE INFLUENCE OF CELL SIZE ON GROWTH RATE,AND CARBON,NITROGEN, CHLOROPHYLL a AND SILICA CONTENT1

The effect of cell size on growth rates and some cellular contents of Thalassiosira nordenskioeldii Cleve has been measured at 0 and 10 C. At 0 C the growth rate did not vary with cell size. The 2 smallest clones at this temperature had reduced growth rates because of the induction of sexuality in that size range. The clones grown at 10 C showed a significant negative relationship between growth rate and valve diameter with the cell surface area/volume ratio positively related to growth rate. At both temperatures the smaller cells had proportionately more carbon and nitrogen/unit cell volume. The amount of chlorophyll a and silica/unit cell surface area increased with increasing cell surface area at both 0 and 10 C. Both the C/N and C/chl a ratios showed no significant change with cell size at either temperature but there was a significant increase in the C/chl a ratio at 0 C. The C/Si ratio decreased with increasing cell size at both 0 and 10 C.     

Flavone 5-O-glucosides from Daphne sericea

The aerial parts of Daphne sericea yielded two new flavonoids, luteolin 7-methyl ether 5-β-d-glucoside and luteolin 7,3′-dimethyl ether 5-β-d-glucoside, as well as luteolin 7-methyl ether, isovitexin, apigenin and its 7-β-d-glucoside.     

Expression of genes for plastid membrane proteins in barley under intermittent light conditions

Barley plants grown under intermittent light show a plastid membrane composition intermediate between those of etioplasts and chloroplasts. In particular protochlorophyll reductase disappears from the membranes whereas the 32000 protein, coded for by chloroplast DNA, becomes integrated into the membranes. The light-harvesting chlorophyll a/b protein does not accumulate within the membranes even after 11 d of development, while the corresponding mRNA can already be observed after 4 d and is translated under in vivo conditions.Abbreviations LHCP light-harvesting chlorophyll a/b protein - IL intermittent light - LD light-dark (12-h day) - EGTA ethyleneglycol-bis(oxy-ethylenenitrile)tetraacetic acid     

Bacteriochlorophyll a cation radical in solution and in reaction centers of Rhodopseudomonas sphaeroides. Resonance Raman scattering

Resonance Raman spectra of the π-cation of bacterio-chlorophyll a in solution at 30 K are reported and discussed. Outer C

C bonds of the pyrroles and the methine bridges are weakened by the ionization, while C

N and Mg-N bonds remain essentially unaffected. Resonance Raman spectra of reaction centers suggest that the positive charge on P-870⁺ should be localized on a single bacteriochlorophyll molecule by the lifetime of the scattering process (≈ 10^?13 s).     

Rubidium—A possible essential trace element

The rubidium content of whole blood was estimated by instrumental neutron activation analysis. In 46 healthy children it amounts to {ie193-1} g/g dry weight. There was no difference between the values found for infants, toddlers, and school children. In 29 dietetically treated patients with phenylketonuria and maple-syrup-urine disease the values were significantly lower than in healthy children. During the first three months of diet therapy the rubidium levels remained in the lower range of the normal values, decreasing to about 60% of the mean of normal values later on. With increasing length of diet therapy these values tended to decrease. It remains questionable whether these decreased levels reflect only an induced biochemical phenomenon without biological importance, or whether they are the first signs of a deficiency syndrome.     

Leukotriene A: stereochemistry and enzymatic conversion to leukotriene B

Leukotriene A was assigned the structure 5(S)-$\text{trans}$-5,6-oxido-7,9-$\text{trans}\text{-11,14-}\text{cis}$-eicosatetraenoic acid by the enzymatic conversion of a synthetic product of known stereochemistry into the naturally occurring isomer of 5(S),12(R)-dihydroxy-6,8,10,14-eicosatetraenoic acid in human polymorphonuclear leukocytes.