Establishment and Growth Kinetics of the Mutant Ehrlich-Lettré Ascites Cell Strain Hd33 In Permanent Suspension Culture1,2

Cells of a mutant in vivo subline of the Ehrlich-Lettré mouse ascites tumour (ELAT) were converted to growth in suspension culture. Kinetic analysis revealed the selective character of the conversion process; without a detectable adaptation period, a fraction of about 2 × 10^-5 of the explanted cells continued to grow in vitro. the resulting, mutant Ehrlich-Lettré ascites cell strain was designated HD33 and propagated uninterruptedly from 1974 on. the corresponding in vivo ELAT subline HD33 was derived from the HD33 ascites cell strain by intraperitoneal retransplantation. In HD33 cell suspension cultures, the population doubling time, the average intermitotic interval, as determined by videomonitoring, and the average duration of the cell cycle, as determined from percentage of labelled mitoses (PLM) data, were all measured at 15 hr. Cell loss and quiescent compartments were insignificant. the duration of the G₁ phase was effectively zero. Both PLM data and [³H]/[¹⁴C] thymidine double-labetling measurements revealed an S-phase duration of between 11 and 12 hr. the G₂ phase lasted 3–5 hr. The HD33 strain differs from comparable suspension strains of wild-type Ehrlich ascites cells in the insignificant role of density-dependent inhibition in growth, and the striking prolongation of the S phase which is associated with an excessive, cytoplasmic storage of glycogen by the mutant cells.     

Pigment interactions in chlorosomes of various green bacteria

Resonance Raman experiments were performed on different green bacteria. With blue excitation, i.e. under Soret resonance or preresonance conditions, resonance Raman contributions were essentially arising from the chlorosome pigments. By comparing these spectra and those of isolated chlorosomes, it is possible to evaluate how the latter retain their native structure during the isolation procedures. The structure of bacteriochlorophyll oligomers in chlorosomes was interspecifically compared, in bacteriochlorophyllc- and bacteriochlorophylle- synthesising bacteria. It appears that interactions assumed by the 9-keto carbonyl group are identical inChlorobium limicola, Chlorobium tepidum, andChlorobium phaeobacteroides. In the latter strain, the 3-formyl carbonyl group of bacteriochlorophylle is kept free from intermolecular interactions. By contrast, resonance Raman spectra unambiguously indicate that the structure of bacteriochlorophyll oligomers is slightly different in chlorosomes fromChloroflexus auranticus, either isolated or in the whole bacteria.     

Structure and mechanism of the magnesium-independent aromatic prenyltransferase CloQ from the clorobiocin biosynthetic pathway

CloQ is an aromatic prenyltransferase from the clorobiocin biosynthetic pathway of Streptomyces roseochromogenes var. oscitans. It is involved in the synthesis of the prenylated hydroxybenzoate moiety of the antibiotic, specifically catalyzing the attachment of a dimethylallyl moiety to 4-hydroxyphenylpyruvate. Herein, we report the crystal structure of CloQ and use it as a framework for interpreting biochemical data from both wild-type and variant proteins. CloQ belongs to the aromatic prenyltransferase family, which is characterized by an unusual core fold comprising five consecutive ααββ elements that form a central 10-stranded anti-parallel β-barrel. The latter delineates a solvent-accessible cavity where substrates bind and catalysis takes place. This cavity has well-defined polar and nonpolar regions, which have distinct roles in substrate binding and facilitate a Friedel-Crafts-type mechanism. We propose that the juxtaposition of five positively charged residues in the polar region circumvents the necessity for a Mg²⁺, which, by contrast, is a strict requirement for the majority of prenyltransferases characterized to date. Our structure of CloQ complexed with 4-hydroxyphenylpyruvate reveals the formation of a covalent link between the substrate and Cys215 to yield a thiohemiketal species. Through site-directed mutagenesis, we show that this link is not essential for enzyme activity in vitro. Furthermore, we demonstrate that CloQ will accept alternative substrates and, therefore, has the capacity to generate a range of prenylated compounds. Since prenylation is thought to enhance the bioactivity of many natural products, CloQ offers considerable promise as a biocatalyst for the chemoenzymatic synthesis of novel compounds with therapeutic potential.     

Arylalkylamine N-acetyltransferase gene expression in retina and pineal gland of rats under various photoperiods

The present study examines how the circadian oscillators in the retina and the suprachiasmatic nucleus (SCN) respond to changes in photoperiod. Arylalkylamine N-acetyltransferase (aa-nat) gene expression studied by quantitative RT-PCR revealed that in adult Sprague-Dawley rats kept under different light-dark (LD) cycles for two weeks the temporal pattern of AA-NAT mRNA expression was identical in retina and pineal gland. In both tissues, the time span between the onset of darkness and the nocturnal rise in AA-NAT mRNA expression was 3 h under LD 20:4, 6 h under LD 12:12, and 15 h under LD 4:20. As aa-nat expression in the pineal gland is regulated by the circadian oscillator in SCN, the results suggest that the photoperiodic differences accompanying the seasons of the year are imprinted in more than one oscillator and that this may accentuate the important message regarding 'time of year.'     

Efficient assembly of photosystem II in Chlamydomonas reinhardtii requires Alb3.1p, a homolog of Arabidopsis ALBINO3

Alb3 homologs Oxa1 and YidC have been shown to be required for the integration of newly synthesized proteins into membranes. Here, we show that although Alb3.1p is not required for integration of the plastid-encoded photosystem II core subunit D1 into the thylakoid membrane of Chlamydomonas reinhardtii, the insertion of D1 into functional photosystem II complexes is retarded in the Alb3.1 deletion mutant ac29. Alb3.1p is associated with D1 upon its insertion into the membrane, indicating that Alb3.1p is essential for the efficient assembly of photosystem II. Furthermore, levels of nucleus-encoded light-harvesting proteins are vastly reduced in ac29; however, the remaining antenna systems are still connected to photosystem II reaction centers. Thus, Alb3.1p has a dual function and is required for the accumulation of both nucleus- and plastid-encoded protein subunits in photosynthetic complexes of C. reinhardtii.