A burst of CO2 from photosynthesizing leaves after a temperature decrease under constant light conditions

A transient CO₂ burst from seedlings of some plant species was observed after a rapid temperature decrease. The magnitude of the CO₂ release depended on initial temperature, oxygen concentration and light intensity. To obtain a maximal value of CO₂ release, the temperature had to decrease by more than 8°C. The phenomenon was detected only in the light, and was confined to C₃ species. It was inhibited by low oxygen concentration, indicating its possible connection with photorespiration.     

Production and release of peptidoglycan and wall teichoic acid polymers in pneumococci treated with beta-lactam antibiotics

Autolysin-defective pneumococci treated with inhibitory concentrations of penicillin and other beta-lactam antibiotics continued to produce non-cross-linked peptidoglycan and cell wall teichoic acid polymers, the majority of which were released into the surrounding medium. The released cell wall polymers were those synthesized by the pneumococci after the addition of the antibiotics. The peptidoglycan and wall teichoic acid chains released were not linked to one another; they could be separated by affinity chromatography on an agarose-linked phosphorylcholine-specific myeloma protein column. Omission of choline, a nutritional requirement and component of the pneumococcal teichoic acid, from the medium inhibited both teichoic acid and peptidoglycan synthesis and release. These observations are discussed in terms of plausible mechanisms for the coordination between the biosynthesis of peptidoglycan and cell wall teichoic acids.     

Topological linkage of circular DNA molecules promoted by Ustilago rec 1 protein and topoisomerase

We studied the formation of linked circular DNA molecules promoted by the combined action of rec 1 protein and type I topoisomerase of Ustilago maydis. When ATP was added as cofactor to reactions containing rec 1 protein, pairs of homologous circular DNA molecules became linked after addition of topoisomerase. Closed circular duplex molecules could be joined at homologous sites with circular single-stranded molecules or with other circular duplex molecules, provided that homologous single-stranded DNA fragments or RNA polymerase and nucleoside triphosphates were also added. Complexes formed were topologically linked through regions of heteroduplex DNA. When the analog adenylyl-imidodiphosphate was substituted for ATP, nonhomologous pairs of circular DNA molecules became linked.     

Studies on the mechanism of intrinsic resistance to beta-lactam antibiotics in group D streptococci

Six penicillin-binding proteins (PBPs) were detected in clinical isolates of each one of three group D streptococci: Streptococcus bovis, S. faecalis and S. faecium. When examined in whole organisms, the PBPs of S. faecium, the most penicillin-resistant species of group D streptococci, generally had lower affinities for the antibiotic than those of S. faecalis (intermediate penicillin resistance), which in turn were of lower affinity than those of S. bovis (penicillin-sensitive). On the other hand, no quantitative correlation could be established between the binding of penicillin to any one PBP or group of PBPs, and the penicillin MIC value for the corresponding micro-organism. Examination of the amounts of antibiotic bound and the rates of binding to PBPs of equal numbers of protoplasts and whole bacteria of S. faecalis and S. faecium, indicated that there was no permeability barrier to benzylpenicillin in the cell walls of these species. The lower antibacterial effectiveness of cephalothin compared with ampicillin in group D streptococci was paralleled by the higher concentrations of cephalothin needed in competition assays to inhibit the lower molecular size PBPs of these bacteria.     

Selective Utilization of Pyrimidine Deoxyribonucleosides for Deoxyribonucleic Acid Synthesis in Pneumococcus

When pyrimidine deoxyribonucleosides are supplied to growing cultures of Diplococcus pneumoniae, they are selectively used for incorporation into deoxyribonucleic acid (DNA). Differently labeled molecules of deoxyuridine, thymidine, and deoxycytidine were used to study the precursor pathways of this organism. Each of these preformed pyrimidine deoxynucleosides is incorporated intact (i.e., without cleavage of the glycosidic bond) and is predominantly recoverable as DNA thymidine. During the utilization of deoxycytidine and deoxyuridine by pneumococci, large proportions of the available precursor are converted to free thymidine, which is secreted back into the growth medium. The biochemical pathways for selective incorporation into DNA and the regulation of concentrations of intracellular thymidine compounds by excretion of free thymidine are discussed.     

Isolation and structure of an intrastrand cross-link adduct of mitomycin C and DNA.

A new covalent mitomycin C-DNA adduct (4) was isolated from DNA exposed to reductively activated mitomycin C (MC) in vitro. The MC-treated DNA was hydrolyzed enzymatically under certain conditions, and the new adduct was isolated from the hydrolysate by HPLC. Its structure was determined by ultraviolet and circular dichroism spectroscopy and chemical and enzymatic transformations conducted on microscale. In the structure, a single 2" beta, 7"-diaminomitosene residue is linked bifunctionally to two guanines in the dinucleoside phosphate d(GpG). The guanines are linked at their N2 atoms to the C1" and C10" positions of the mitosene, respectively. A key to the structure was a finding that removal of the mitosene from the adduct by hot piperidine yielded d(GpG); another was that the adduct was slowly converted to the known interstrand cross-link adduct 3 by snake venom diesterase and alkaline phosphatase. Adduct 4 represents an intrastrand cross-link in DNA formed by MC. Of the two possible strand-polarity isomers of 4, 4a in which the mitosene 1"-position is linked to the 3'-guanine of d(GpG) is designated as the proper structure, on the basis of the mechanism of the cross-linking reaction. The same adduct 4 was isolated from poly(dG).poly(dC), synthetic oligonucleotides containing the GpG sequence, and Micrococcus luteus and calf thymus DNAs. The relative yields of interstrand and intrastrand cross-links (3 and 4) were determined under first-order kinetic conditions; an average 3.6-fold preference for the formation of 3 over that of 4 was observed. An explanation for this preference is proposed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular structure of rare but geographically widespread sn-glycerol-3-phosphate dehydrogenase ‘ultra-fast’ electrophoretic alleles in Drosophila melanogaster

Six naturally occurring but rare alleles of sn-glycerol-3-phosphate dehydrogenase (Gpdh) in Drosophila melanogaster have been investigated in this study. They all belong to a class of Gpdh ^UF (ultra-fast) alleles, because their electrophoretic mobilities are faster than that of the Gpdh ^F (fast) allele. The Gpdh ^UF variants are widespread, and have been reported from five continents. DNA sequence analysis has shown that the change in electrophoretic mobility was in each allele caused by a single amino acid residue substitution in the encoded protein. In the Xiamen ^UF allele it is a substitution of lysine (AAA) to asparagine (AAT) in exon 1 (residue 3). An asparagine (AAT) to aspartate (GAT) change was found in exon 6 (residue 336) in the Iowa ^UF and Netherlands ^UF alleles. The mobility of the Raleigh ^UF allele was altered by a valine (GTG) to glutamate (GAG) substitution in exon 3 (residue 76). Two mutations were detected in the Brazzaville ^UF allele: a lysine (AAG) to methionine (ATG) substitution in exon 2 (residue 68) is responsible for the ultra-fast phenotype of this variant, while a tyrosine (TAT) to phenylalanine (TTT) substitution in exon 4 (residue 244) is not expected to alter the electrophoretic mobility of the encoded protein. These results indicate that the Gpdh ^UF alleles originate from different mutational events, and only two of them — Iowa ^UF and Netherlands ^UF — might share a common ancestry. The GPDH activity of the Iowa ^UF allele is intermediate between those of the Gpdh ^S and Gpdh ^F control stocks. The other Gpdh ^UF variants have lower activities than the controls: Xiamen ^UF -83%, Raleigh ^UF -80% and Brazzaville ^UF -73% of the Gpdh ^F control.     

Sigma-B, a putative operon encoding alternate sigma factor of Staphylococcus aureus RNA polymerase: molecular cloning and DNA sequencing.

We have identified a gene cluster located on the chromosomal SmaI I fragment of a highly methicillin resistant strain of Staphylococcus aureus, consisting of four open reading frames (ORFs), named after the number of deduced amino acid residues, in the sequential order orf333-orf108-orf159-orf256. The gene cluster showed close similarities to the Bacillus subtilis sigB operon both in overall organization and in primary sequences of the gene products. The complete gene cluster (provisionally named sigma-B or sigB) was preceded by an sigmaA-like promoter (PA) and had an internal sigmaB-like promoter sequence (PB) between orf333 and orf108, suggesting a complex regulatory mechanism. The polypeptides encoded by orf333, -108, -159, and -256 showed 62, 67, 71, and 77% homologies, respectively, with the RsbU, RsbV, RsbW, and SigB polypeptides encoded by the B. subtilis sigB operon. A Tn551 insertional mutant, RUSA168 (insert in orf256 of the staphylococcal sigma-B operon), showed drastic reduction in methicillin resistance (decrease in MIC from 1,600 microg ml-1 to 12 to 25 microg ml-1off