Suppression of temperature-sensitive aminoacyl-tRNA synthetase mutations by ribosomal mutations: A possible mechanism

Summary The biochemical basis of suppression of a temperature-sensitive alanyl-tRNA synthetase (alaS) mutation by mutational alterations of the ribosome has been investigated. Measurement of the polyU-dependent polyphenylalanine synthesis showed that ribosomes from the suppressor strains are less active than ribosomes from the unsuppressed aminoacyl-tRNA synthetase mutant. In this system no increased translational ambiguity could be detected for the suppressor ribosomes. This fact and also the findings that the ram-1 mutation is not able to suppress the aminoacyl-tRNA synthetase mutation and that presence of the suppressor allele is not accompanied by a measureably improved alanyl-tRNA synthetase activity argue against the possibility that suppression might be due to increased translational misreading rates of the alanyl-tRNA synthetase mRNA.It has been further found that partial suppression of temperature sensitive growth of the alaS mutation can be achieved by independent ribosomal mutations leading to reduced growth rates because of a mutation to antibiotic resistance. Addition of low concentrations of a variety of antibiotics acting at the ribosomal level can also partially revert the temperature-sensitive phenotype of the alaS mutant. Although the possibility cannot be excluded that suppression is due to the stabilisation or activation of the mutant enzyme by some indirect effect of the suppressor ribosomal mutations, the following working hypothesis is favoured at the moment: It is assumed that limitation of the aminoacyl-tRNA synthetase activity in a certain range of the restrictive temperature causes growth inhibition by the premature termination of polypeptide synthesis at the ribosome or by the unbalanced synthesis of the individual cellular proteins under this condition. The mechanism of suppression by ribosomal mutations is proposed to consist of the release of this growth inhibition by the reduction of the rate of polypeptide synthesis, which would keep amino acid incorporation from exceeding the slow charging of tRNA and thus exhausting the pool of charged tRNA. In the suppressor strains, therefore, growth at the semi-restrictive temperature is no longer limited by the aminoacylation of tRNA but by the translational process at the mutated ribosome. This influence of the ribosomal mutation on the speed of translation could be directly or indirectly coupled with an effect on translational fidelity resulting in the prevention of the binding of uncharged or non-cognate charged tRNA or in the tighter binding of peptidyl-tRNA when cognate aminoacyl-tRNA is limiting.     

New types of islet cells in a cyclostome,Petromyzon marinus L.

Four types of acidophilic granular cells, in addition to B-cells, are identified in the islet organ of anadromous specimens of two subspecies of Petromyzon marinus by light and electron microscopy. Three of these acidophils (PI, PII and PIV-cells) occur in both the cranial and hepatic islets while a fourth type (PIII-cell) has only been found in the hepatic islet of some animals. The granules of the PI-cells stain with ponceau de xylidine, give a distinct tryptophan reaction and in ultrastructural examination show large, dense granules. The PII-cells contain unusual crystals and appear to be a non-secretory stage of the PI. The PIII-cells stain deep-red and acid fuchsin. They contain very large, dense granules and some lysosomes. PIV-cells stain selectively with phosphotungstic acid-hematoxylin and ultrastructurally, contain small, more or less dense granules. It appears that PI- and PIV-cells develop directly from B-cells, while the PIII-cells derive from PI-cells. despite their direct or indirect origin from B-cells, the PI-, PIII- and PIV-cells show characteristic features of functionally independent endocrine cells. Petromyzon marinus may be an ideal model for the understanding of phylogenetic and pathological interrelationships between islet and gastrointestinal hormones. It is clear that the interpretation of the islet organ of the cyclostomes, which has been generally considered a source of insulin only, requires a revaluation.     

Einige endokrinologische Besonderheiten der V?gel

Zusammenfassung Anhand neuer embryologischer, morphologischer, physiologischer und biochemischer Befunde werden die vogelspezifischen Eigentümlichkeiten von drei endokrinen Systemen diskutiert: Pinealkomplex, hypothalamo-hypophysäres System und gastrointestinales Endokrinium.Trotz der allgemein besonders starken Beeinflußbarkeit der Vögel durch photoperiodische Veränderungen ist bei ihnen der Pinealkomplex zu einer intracranialen endokrinen Drüse reduziert. Diese Epiphyse (Pinealorgan) zeigt unter experimentellen Bedingungen eine außerordentliche Unabhängigkeit von photoperiodischer Steuerung. Das völlige Fehlen des Pinealkomplexes bei den relativ nahe verwandten Krokodilen deutet auf die Möglichkeit hin, daß dies wohl eher phylogenetisch als funktionell zu erklären ist.Das hypothalamo-hypophysäre System ist im wesentlichen reptilienartig, zeigt aber drei auffallende Spezialisierungen: 1. Eine hochentwickelte Eminentia mediana, welche aus zwei getrennten Regionen besteht. 2. Die Pars distalis ist mit der Eminentia so verbunden, daß ihre beiden Unterabteilungen (cephaler und caudaler Lappen) von beiden Regionen der Eminentia über getrennte Portalgefäße versorgt werden. 3. Den Vögeln als Gruppe fehlt die Pars intermedia.Die auffallendsten Besonderheiten des gastrointestinalen Endokriniums stehen mit dem Inselorgan in Verbindung: insulinproduzierende B-Zellen und glukagonbildende A-Zellen sind weitgehend in besondere Inseln getrennt. Im Gegensatz zu dem der anderen Tetrapoden ist das Fettgewebe der Vögel insulin-unempfindlich. Die endokrine Kontrolle des Fettgewebes erfolgt über eine indirekte anabole Route (durch prolaktinstimulierte Lipogenese in der Leber) sowie eine direkte katabole Route durch Pankreasglukagon.Bei einem Vergleich mit anderen Gnathostomengruppen zeigen Epiphyse, Adenohypophyse und Inselorgan einen besonders starken Trend zur Unabhängigkeit von direkter Innervation. In bezug auf Adenohypophyse und Inselorgan repräsentieren dabei die Vögel das entgegengesetzte Extrem zu den Knochenfischen (Teleostier), bei denen diese Drüsen besonders stark innerviert sind.Die Vögel und Teleostier werden kurz mit den Myxiniden verglichen, deren endokrines System besonders schwach entwickelt ist. Die Unterschiede zwischen den drei Gruppen werden durch drei verschiedene Wege der Anpassung an Umweltbedingungen gedeutet: 1. Aktive Anpassung durch ein hochentwickeltes neuro-endokrines Kontrollsystem (Teleostier). 2. Passive, osmokonforme Anpassung, welche ein stark entwickeltes Endokrinium überflüssig macht (Myxiniden). 3. Vermeidung ungünstiger Umweltbedingungen durch Flugvermögen; eine verfeinerte, sekretomotorische Kontrolle der endokrinen Drüsen des normalen Stoffwechsels ist unnötig (Vögel).

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Some endocrine specializations of the birds

Summary Against the background of recent embryological, morphological, physiological and biochemical studies, peculiarities of three different avian endocrine systems are discussed: pineal complex, hypothalamo-hypophysial system, and gastrointestinal endocrine system.Despite the marked photosensitivity of the birds in general, their pineal complex is reduced to an intracranial pineal gland, which shows a very high degree of functional autonomy when released from photoperiodic control. The complete absence of the pineal complex in the alligators suggests that this may be due to phylogenetic rather than adaptive reasons.The hypothalamo-hypophysial system is basically of reptilian type, but shows three marked specializations: (1) the highly developed median eminence consists of two distinct regions; (2) the Pars distalis is located so, that both of its subdivisions (cephalic and caudal lobe) appear to receive distinctly separate vascularisation from the median eminence; (3) the birds as a group lack a Pars intermedia.Within the gastrointestinal endocrine system of birds, the most obvious peculiarities identified so far are connected with the islet organ: insulin-producing B-cells and glucagonproducing A-cells are largely separated in different islets, and contrary to the situation in other tetrapodes, the avian adipose tissue is insulin-insensitive. The endocrine control of the adipose tissue involves an indirect anabolic route via prolactin-induced hepatic lipogenesis, and a direct catabolic route, via pancreatic glucagon.When compared with other groups of gnathostomes, the pineal gland, adenohypophysis and islet organ of the birds show a particularly strong trend towards independence from secretomotor innervation. With respect to the adenohypophysial and islet innervation, the birds represent the opposite extreme to the teleosts, whose adenohypophysis and islet organ are particularly well innervated.Birds and teleosts are compared with the Myxinidae, whose endocrine system is particularly poorly developed. It is hypothesized that the differences between the endocrine systems of these three groups reflect three different ways of adjustment to environmental conditions: (1) teleosts actively adjust to a continuous challenge from external osmolarity, whose control has to be integrated with the milieu interne and nutritional factors. They developed a highly sophisticated control system of their endocrines, which is capable of overriding humoral stimuli by nervous interference. (2) The Myxinidae passively conform with the osmotic environment, which makes a highly developed endocrine control system unnecessary. (3) The birds are shielded from environmental factors by a specialized body surface, and they can easily avoid unfavorable conditions by flight. This makes a sophisticated and fast acting (i.e. nervous) control of such endocrines unnecessary, which are involved in the maintenance of the normal milieu interne.Wir danken MissKathleen Matt für die Hilfe bei der Anfertigung der Zeichnungen.

     

Vegetative innervation of the esophagus. II. Intraganglionic laminar endings.

The intraganglionic laminar endings in the esophagus of the cat and the rhesus monkey show absolute equivalence between the results in both species from the morphological standpoint. The different types of apparatus found are described, with their location in the esophagus and their percentage distribution in relation to the different portions of its wall. The osmium tetroxide-zinc iodide technique gives pictures equivalent to those using silver impregnations, with the added advantage that the former brings out the morphological details more clearly, to the point of showing up the peculiar characteristics of the edges with their thorn-like protrusions. The complete independence of these structures within the ganglion is confirmed, and evidence is provided for rejecting the possibility that they might be dendritic prolongations of the neuronal elements composing the intramural ganglia. A possible afferent function is proposed, which, however, must be considered an open question, pending the results of further experimental investigation.     

α-Mannosidases of generaAspergillus andRhizopus. Activity and capacity to utilizeSaccharomyces cerevisiae mannan of the best α-mannosidase producerAspergillus flavus link 69

Strains of fungi imperfecti of generaAspergillus andRhizopus were tested for the ability to produce α-mannosidases. The most suitable α-mannosidase producer of a total of 20 strains under study wasAspergillus Ravus Link 69. The parameters studied during the cultivation included the growth rate expressed as cell dry weight, α-mannosidase activity of the extracellular medium withp-nitrophenyl α-D-mannopyranoside as substrate, and utilization ofSaccharomyces cerevisiae mannanvia its disappearance from the cultivation medium.     

The part played by the mucopolysaccharides in the form birefringence of the Collagen

We stressed in our wourk the necessity of knowing the details of the interaction between the acid mucopolysaccharides and the collagen. Employing the appropriate methods we carried out the measurements of birefringence of strictly limited parts of collagen bundles. The measurements were carried out before and after the collagen bundles were subjected to the action of testicular hyaluronidase.The statistic study of the data we arrived have revealed that the testicular hyaluronidase which removes the acid mucopolysaccharides causes a decrease of form birefringence.These results are discussed on the regard to former research with done by the author and the conclusions may be drawn that the acid mucopolysaccharides play a part in the form birefringence of collagen bundles, and therefore have a macromolecular orientation.The author is indebted to Prof. Lucien Lison who has done the statistical processing.