Studies on the fine structure of puffs in Sciara coprophila

Fine structure of RNA and DNA puffs of Sciara coprophila was studied during late developmental stages of the fourth larval instar. In RNA puffs the predominant structure seen seems to be a diffuse, lampbrush-like thread or threads sectioned in a variety of planes. The thread is composed of filamentous and granular material. Three types of RNA puffs, each with a slightly different morphology, are found. In their development DNA puffs pass through a precise sequence of stages, each with its distinct morphologic and metabolic characteristics. At the initial and final stages, when much of the puff chromatin is in the compacted state, DNA puffs resemble condensed chromosomal bands. In contrast, at stages when most chromatin is diffuse, DNA puffs share many structural characteristics of RNA puffs. Most of the expanded puff area is permeated by lampbrush-like threads composed of fibrils and granules. RNA and DNA puffs were compared with respect to granule size and distribution by means of electron micrographs of known magnification. The results of the statistical analysis show that: 1) The coefficient of variation (C.V.) of the method of measurement falls between 5 and 7%. 2) There is a fluctuation in granule sizes within each puff with a C.V. of 24–26%. 3) The average granule diameter is 238 Å for DNA puffs and 310 Å for RNA puffs; the difference is statistically significant. 4) The variation in mean granule size in a sample of DNA puffs is rather small (C.V. 12%), while the variation in granule size between different RNA puffs is somewhat larger (C.V. 20%). 5) The relative spread of granule sizes in DNA puffs is more restricted than that in RNA puffs. It is evident then that, on the average, DNA puff granules are smaller and more uniform than granules found in RNA puffs.     

Helix–coil transition in poly(γ-benzyl-L-glutamate) and poly-ε-carbobenzoxy-L-lysine

In this paper two points are considered: the methods of evaluating the helical content θ and the calculation of the parameters of the transition from experimental data and its interpretation. The parameter ΔH obtained is in good agreement with the calorimetric one and v is found to be independent of temperature and solvent and in agreement with the ordinarily accepted value for poly(γ-benzyl-L -glutamate). The different methods of estimating θ are discussed for both polypeptides.     

Structural and immunological studies on the protoplast membrane of the yeast Candida utilis

Cell membranes of the yeast Candida utilis isolated by lysis of protoplasts have been shown to be lipoprotein in nature. Electron microscopy shows that Mg⁺⁺ is responsible for maintaining the integrity of the membrane. A close serological relationship was found between membranes and cell walls isolated from the yeast. This relationship was exhibited not only by membranes obtained by strepzyme treatment but also by those obtained from the action of helicase enzyme. No such relationship existed between membranes and whole cells. Related data have been obtained by treatment of yeasts with different digestive enzymes. All of the results suggest that the protoplast membrane possesses traces of structural cell wall material. This material is detectable by serological tests, but not by electron microscopy.     

Preparation of protoplast-like structures from conidia ofFusarium culmorum

Protoplast-like structures have been formed by digestion of the cell walls ofFusarium culmorum conidia by lytic enzyme preparations ofMicromonospora AS. Under the test conditions extrusion of the protoplasts was not observed. It seems that digestion of the cell wall occurs in different stages. Digestion of the septa preceded the formation of protoplasts of the individual cells of the multicellularF. culmorum conidia. A few protoplasts survived the lytic enzyme treatment. “Protoplasts” obtained from conidia are much more stable than those obtained from young hyphae and were able to germinate with the formation of normal mycelium. Lysis of some of the protoplast bodies led to the formation of a membranous structure. The protoplasts derived from each of the constituent cells of the conidia could be isolated with the micromanipulator. No differences were found in the ability of the isolated cells to germinate.     

Atrial natriuretic factor in the vena cava and sinus node

We investigated the localization of atrial natriuretic factor (ANF) mRNA and of immunoreactive ANF in the vena cava and sinus node of rat and, for comparative purposes, in atria and ventricles. In situ hybridization with an ANF cRNA probe revealed that the supradiaphragmatic portion of the inferior vena cava contains almost as much mRNA as the atria, whereas the levels were less in the superior vena cava and higher than in ventricles in the sinus node. Immunoreactive ANF (high Mr form) was found to be 22 times less abundant in the supradiaphragmatic vena cava and 148 times less abundant in the superior vena cava than in atrial cardiocytes. The wall of the supradiaphragmatic portion of the vena cava and the valve (eustachian valve) that separates the atrial cavity from that of the vein are made up of atrial-like cardiocytes containing secretory granules. The subendothelial area of the superior vena cava also contains atrial-like cardiocytes with secretory granules, whereas the outer portion of the vein is made up of "transitional cells" without or with only a few secretory granules. Secretory granules in the vena cava and nodal cells, as well as transitional cells, contain immunoreactive ANF. With immunocryoultramicrotomy, virtually all cells, whether atrial-like, transitional, or nodal, and even those without secretory granules, were found to contain immunoreactive ANF in their Golgi complex and in secretory vesicles in the vena cava and in the sinus node.     

Cooperation of v-jun and v-erbB oncogenes in embryo fibroblast transformation in vitro and in vivo.

Retroviral vectors carrying either the v-jun and v-erbB sequences or the v-jun gene linked to the neomycin resistance gene were constructed on the basis of the structural genome organization of avian erythroblastosis virus (AEV). These viruses, called JB and JN, respectively, were rescued as Rous-associated virus-1 pseudotypes, and they were shown to successfully transform chicken embryo fibroblasts in vitro. However, in agar, colonies developed from JB-infected fibroblasts were three to five times larger than those obtained after infection with JN or with AEV Pst124 carrying only a functional v-erbB gene. In vivo, on chorioallantoic membrane (CAM) assays, JB produced fibrosarcomas that were more rapidly growing and much larger than those induced by JN or AEV Pst124. Moreover, in chickens infected in ovo with JB, multiple fibrosarcomas arose in different organs a few days after birth, whereas no tumor could be detected in parallel experiments in either JN- or AEV Pst124-infected animals. These results demonstrate that in embryo fibroblast cells, v-jun and v-erbB can act synergistically to enhance the transformation potential of either oncogene alone both in vitro and in vivo.     

The acquisition of increased insulin-responsive hexose transport in 3T3-L1 adipocytes correlates with expression of a novel transporter gene

The expression of two genes encoding facilitated glucose transporter proteins was studied during the differentiation of the 3T3-L1 fibroblastic cell line into adipocytes. The mRNA encoding the widely expressed HepG2/brain glucose transporter (GTI) is detectable in fibroblasts and its abundance remains unchanged during differentiation. On the other hand, the mRNA encoding a glucose transporter protein (GTIII) localized exclusively to muscle and adipose tissue is undetectable in fibroblasts but present in adipocytes. GTIII mRNA is first expressed three days after differentiation of 3T3-L1 cells has begun. Similarly, it is not until 3 days following the initiation of differentiation that GTIII protein can be detected, as assayed either by Western immunoblot or indirect immunofluorescence. The latter technique localizes GTIII predominantly to the perinuclear region of the adipocyte. The appearance of GTIII in developing fat cells correlates temporally with the acquisition of an increased stimulation of hexose uptake by maximal concentrations of insulin. These data support the concept that the marked increase in hexose transport in adipocytes in response to insulin is dependent on the expression in these cells of a specific, hormone-regulatable transport protein.     

An evolutionarily conserved enzyme degrades transforming growth factor- alpha as well as insulin

A single enzyme found in both Drosophila and mammalian cells is able to selectively bind and degrade transforming growth factor (TGF)-alpha and insulin, but not EGF, at physiological concentrations. These growth factors are also able to inhibit binding and degradation of one another by the enzyme. Although there are significant immunological differences between the mammalian and Drosophila enzymes, the substrate specificity has been highly conserved. These results demonstrate the existence of a selective TGF-alpha-degrading enzyme in both Drosophila and mammalian cells. The evolutionary conservation of the ability to degrade both insulin and TGF-alpha suggests that this property is important for the physiological role of the enzyme and its potential for regulating growth factor levels.