Polyamines and protein synthesis: Studies in various polyamine-requiring mutants ofEscherichia coli

Summary DifferentEscherichia coli mutants auxotrophic for polyamines were studied in order to investigate the relationships among polypeptide synthesis in cell-free systems, ribosomal distribution profiles and endogenous polyamine pools. Thein vitro protein synthetic activity and the polyribosomal content were reduced in extracts from putrescine-starved cells of the double mutants MA 255 and MA 261, but not in the arginine-conditional auxotroph DK 6. Putrescine addition to the cultures of all these strains previously starved for polyamines, provoked a shift towards monomers in the equilibrium involving ribosomal particles. Concomitant changes in the intracellular levels of polyamines were observed: putrescine and spermidine increased markedly, and cadaverine disappeared.Dedicated to ProfessorLuis F. Leloir on the occasion of ths 70^th birthday.     

Characterization of glycerol nonutilizing and protoperithecial mutants ofNeurospora

Summary Mutants defective in polyol metabolism and/or in protoperithecial development were selected inNeurospora tetrasperma, a species in which protoperithecial development occurs at nonpermissively high temperature if certain polyols are used in lieu of sucrose as carbon source. Mutants selected for nonutilization of one of the four polyols tested, glycerol, mannitol, sorbitol, or xylitol, were usually found to be nonutilizers of the other three polyols as well. Mutants blocked at various stages of protoperithecial development complemented pairwise to produce more advanced developmental stages, usually mature protoperithecia and, when of opposite mating type, mature perithecia. About one-third of the mutants manifested both polyol auxotrophy and defective protoperithecial development upon initial isolation, but protoperithecial defectiveness in such mutants usually showed erratic segregation in crosses and/or instability to repeated vegetative transfer, whereas polyol auxotrophy usually did not and was, therefore, studied further. Two glycerol nonutilizing strains were introgressed intoN. crassa to facilitate genetic analysis. One,glp-4, lacked both inducible and constitutive glycerol kinase and mapped to linkage group VI, betweenad-1 andrib-1; the other,glp-5, lacked glyceraldehyde kinase and mapped to linkage group I, proximal toad-9. Another mutant,gly-u(234), has been reported by other investigators to lack inducible glycerol kinase but to map to linkage group I, distal toad-9.     

Calf development and mother-calf spatial relationships in Southern right whales

Changes in spatial relationships between mother and calf right whales (Eubalaena australis) from birth to the separation of yearling calves from their mothers were observed. During the first few weeks of a calf's life, mother and calf were within close proximity over 90% of the time, and mothers were responsible for maintenance of contact with their infants. Later calves strayed farther and initiated many more leaves and approaches than their quiescent mothers. The mothers still maintained contact with their infants. Just before migration away from the area, pair members resumed close proximity and leaves and approaches by both diminished. Yearling calves, returning to the area with their mothers after six months, stayed close to their mothers and few leaves and approaches by either pair member were recorded. The yearling calves were responsible for maintaining contact as the mothers left them more than approached them. This behaviour on the part of mothers probably contributed to weaning of yearlings and separation after a few weeks in the area.     

Metabolism of Guanine and Guanine Nucleotides in Primary Rat Neuronal Cultures

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduced intracellular content of methotrexate in an isolated MTX-resistant cell line of Nicotiana plumbaginifolia

Communicated by R. N. Beachy     

Structural Characteristics of the Short-Tail Fibers of T4 Bacteriophage

The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure.     

Marker rescue transformation by linear plasmid DNA in Bacillus subtilis

Although plasmid-free Bacillus subtilis cannot be transformed for markers carried by linear or nicked plasmid DNA, a resident plasmid can rescue a marker on such damaged DNA under certain conditions. Linearized chimeric plasmid DNA has been used to transform cultures carrying a resident plasmid which is homologous with a portion of the donor. This system has revealed the following properties of the marker rescue process: (1) It is recE dependent. (2) It requires the presence in the resident plasmid of sequences which are homologous to the donor. (3) When the selected marker is on a nonhomologous segment it must be flanked by segments which are homologous to the resident plasmid. (4) The efficiency of rescue varies in a regular way with the position of the linearizing cut. (5) Marker rescue is first order with respect to DNA concentration. These properties and other data are interpreted as providing a strong indication that marker rescue occurs by recombination, although an alternative explanation involving recE-dependent recircularization of the donor plasmid has not been eliminated. Our results also suggest that if the major pathway of marker rescue is by recombination, an average of 0.15 Mdal (single strand) must be removed from each donor DNA molecule or otherwise rendered unavailable for recombination and that the exchange frequency during transformational recombination is approximately 0.2 to 0.5 Mdal⁻¹.     

Exome sequencing in multiplex families with left-sided cardiac defects has high yield for disease gene discovery

Congenital heart disease (CHD) is a common group of birth defects with a strong genetic contribution to their etiology, but historically the diagnostic yield from exome studies of isolated CHD has been low. Pleiotropy, variable expressivity, and the difficulty of accurately phenotyping newborns contribute to this problem. We hypothesized that performing exome sequencing on selected individuals in families with multiple members affected by left-sided CHD, then filtering variants by population frequency, in silico predictive algorithms, and phenotypic annotations from publicly available databases would increase this yield and generate a list of candidate disease-causing variants that would show a high validation rate. In eight of the nineteen families in our study (42%), we established a well-known gene/phenotype link for a candidate variant or performed confirmation of a candidate variant’s effect on protein function, including variants in genes not previously described or firmly established as disease genes in the body of CHD literature: BMP10, CASZ1, ROCK1 and SMYD1. Two plausible variants in different genes were found to segregate in the same family in two instances suggesting oligogenic inheritance. These results highlight the need for functional validation and demonstrate that in the era of next-generation sequencing, multiplex families with isolated CHD can still bring high yield to the discovery of novel disease genes.     

Ten simple rules to host an inclusive conference

Conferences are spaces to meet and network within and across academic and technical fields, learn about new advances, and share our work. They can help define career paths and create long-lasting collaborations and opportunities. However, these opportunities are not equal for all. This article introduces 10 simple rules to host an inclusive conference based on the authors’ recent experience organizing the 2021 edition of the useR! statistical computing conference, which attracted a broad range of participants from academia, industry, government, and the nonprofit sector. Coming from different backgrounds, career stages, and even continents, we embraced the challenge of organizing a high-quality virtual conference in the context of the Coronavirus Disease 2019 (COVID-19) pandemic and making it a kind, inclusive, and accessible experience for as many people as possible. The rules result from our lessons learned before, during, and after the organization of the conference. They have been written mainly for potential organizers and selection committees of conferences and contain multiple practical tips to help a variety of events become more accessible and inclusive. We see this as a starting point for conversations and efforts towards building more inclusive conferences across the world. * Translated versions of the English abstract and the list of rules are available in 10 languages in S1 Text: Arabic, French, German, Italian, Japanese, Korean, Portuguese, Spanish, Tamil, and Thai.