High recombination between the breakpoint of a reciprocal translocation in rye (Secale cereale L.) and an interstitially located gene

Summary The recombination fraction between the interstitially located gene an and interchange 303 of rye was found to be 0.244±0.038 in a test cross using the translocation as the male parent. In first metaphase translocation configurations in pollen mother cells of the same plant, the chiasma frequency between an and the translocation breakpoint was found to be significantly more than twice the recombination fraction. Recombination was concluded to be masked by a difference in the alternate frequency between configurations without interstitial chiasmata and configurations with interstitial chiasmata, the effect of the first type being of major importance. Random centromere orientation of translocation multivalents with interstitial chiasmata was concluded to be a realistic assumption. The exceptionally high recombination between an and translocation 303 is discussed. Consideration is also given to the use of interchanges in the establishment of a marker's chromosomal position, and to the use of translocation chromosomes in balanced systems for hybrid breeding purposes.     

Ultrastructural and biological characterization of human choroid cell cultures transformed by Simian Virus 40

A human diploid cell line of choroid origin was isolated from the retrouveal portion of an enucleated eye and designated HC. After 10 passages, when the proliferative capacity of HC cells decreased, they were infected and transformed by Simian Virus 40 (SV40). A proliferating long-term cultured cell line designated HC/SV40 was established and it has been maintained as monolayer for more than 100 passages so far. The two cell lines, HC and HC/SV40, were compared for growth characteristics, capacity to form colonies in soft agar, presence of nuclear T-antigen, and ultrastructure. Cytogenetic analysis was also performed to determine the presence of chromosomal aberrations due to the permanent viral transformation of the cell line. The results indicate that HC/SV40 should be considered the transformed counterparts of HC cells because they are morphologically similar to the latter but can grow in soft agar, possess T-antigen, and show a pattern of karyotypic changes similar to that induced by SV40 in human fibroblasts. The choroid origin of HC and HC/SV40 cell lines was confirmed by the presence, in their cytoplasm, of typical electron dense granules. Their neural origin will make these cell lines very useful for neuropharmacological and differentiation studies.     

Relationship of the replication and incompatibility genes of an IncFVI haemolysin plasmid with other F-like haemolysin plasmids

The replication and incompatibility region of the IncFVI plasmid pSU502 has been isolated by in vitro DNA manipulation as part of a 12.6 kb plasmid, denominated pSU503. Plasmid pSU503 was strongly incompatible with its parental plasmid, pSU1, but was fully compatible with the haemolytic plasmids pSU316 (IncFIII/IV), pHly152 (IncI2) and pSU233 (Inc-pSU233). Furthermore, the 6.9 kb EcoRI fragment of pSU503 which carries the replication and incompatibility determinants of pSU1 did not show any detectable homology (less than 70%) with any of the haemolysin-determining plasmids with which it is compatible. Thus, homologous haemolysin determinants have become linked to apparently unrelated replicons.     

Rapid,gregarious settlement of the larvae of the marine echiuran Urechis caupo Fisher & MacGinitie 1928

Larvae of Urechis caupo Fisher & MacGinitie, reared in the laboratory, were exposed to potential settlement stimuli, including natural sediment from adult burrows, and “scent” obtained from the skin of adult animals. Competent larvae settled rapidly and specifically in response to adult burrow sediment when compared with their responses to other natural and abiotic sediments. Larvae also responded specifically to chemical “scent” from adult animals when the “scent” of another echiuran worm, Listriolobus pelodes Fisher served as a control. Larval responses to chemical “scent” were as great as their responses to natural burrow sediment. Hence, it is likely that larvae settle gregariously in nature in response to “scent” on sediment grains of adult burrows. The chemical “scent” had a molecular weight between ≈3500 and 14000 daltons, as determined by dialysis. It quickly lost its effectiveness in promoting settlement after it was heated to 80 °C, but was relatively stable at ambient ocean temperatures, retaining its effectiveness for several days. It was soluble in sea water. However, larvae did not respond to the chemical “scent”, unless it was adsorbed onto a surface. Purely tactile stimuli, such as the shape, texture, and size-distribution of particles, were not important settlement cues during these experiments.     

Ecdysteroids in the haemolymph and the ovaries of the firebrat Thermobia domestica (Packard) (Insecta,Thysanura): Correlations with integumental and ovarian cycles

Ecdysteroids were analysed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) in females of the apterygotous insect Thermobia domestica, which ahs overlapping moulting and reproductive cycles. During each moulting cycle, a peak in the haemolymph concentration of ecdysteroids occurs at day 9 (in the 11-day standard cycle), which can be correlated with apolysis and the beginning of new cuticle deposition. The ovaries show a peak of ecdysteroids at day 5 (i.e. one day before egg-laying), which suggests that these hormones are also involved in the reproductive cycle. In both cases, HPLC analysis combined with RIA suggests that the main ecdysteroid is 20-hydroxyecdysone. This duality in the function of ecdysteroids is discussed.     

Action of two juvenile hormone antagonists on lepidopteran epidermis

The juvenile hormone antagonist ETB (ethyl-4-2(t-butylcarbonyloxy)-butoxybenzoate) caused formation of precocious larval-pupal intermediates after the 4th (penultimate)-larval instar of the tobacco hornworm, Manduca sexta, when 50 μg were applied to any 3rd stage larvae or to 4th stage larvae within 12 hr after ecdysis. This dose was most effective within 12 hr after ecdysis to the 3rd stage. In the black mutant larval assay for juvenile hormone, ETB had activity, 0.75 μg per larva giving half-maximal score. In vitro ETB acted as a juvenile hormone to prevent the ecdysteroid-induced change in commitment at concentrations above 0.1 μg/ml with an ED₅₀ at 2.8 μg/ml and as a partial juvenile hormone antagonist to 0.1 μg/ml juvenile hormone I at concentrations between 10^?3 and 10^?2 μg/ml. By contrast, EMD (ethyl-E-3-methyl-2-dodecenoate) had little juvenile hormone-like activity in vitro up to its limits of solubility (100 μg/ml) and exhibited sporadic partial juvenile hormone antagonistic activity in vitro at concentrations between 1 and 100 μg/ml. Since these concentrations were 10–1000 times that of juvenile hormone I in the medium, EMD apparently is not an efficient competitor.     

Effects of decapitation and ovariectomy on the regulation of juvenile hormone synthesis in the cockroach, Diploptera punctata

Corpora allata from Diploptera punctata females at adult ecdysis or at the end of the last-larval stadium, when implanted into decapitated females, underwent a cycle of juvenile hormone synthesis similar in timing and magnitude to that of glands implanted into control animals which had been starved and allatectomized. Starvation did not alter the cycle in rates of juvenile hormone synthesis of sham-operated animals.Decapitation of ovariectomized animals resulted in no cycle in rates of juvenile hormone synthesis by implanted adult corpora allata; however, implantation of an ovary along with the corpora allata into decapitated, ovariectomized hosts resulted in a cycle of juvenile hormone synthesis. In control animals, which retained their heads but were starved and allatectomized as well as ovariectomized, the implanted corpora allata showed a cycle of juvenile hormone synthesis only when implanted with an ovary. The maximal rates of juvenile hormone synthesis by the corpora allata in both experimental and control conditions were lower than normal, likely due to the repeated trauma of surgery. However, at no time from eclosion to the end of the first gonotrophic period was the brain necessary for the cyclic response of the corpora allata to the presence of the ovary.     

Comparison of AMP and NADH binding to glycogen phosphorylase b

The binding sites for the allosteric activator, AMP, to glycogen phosphorylase b are described in detail utilizing the more precise knowledge of the native structure obtained from crystallographic restrained least-squares refinement than has hitherto been available. Localized conformational changes are seen at the allosteric effector site that include shifts of between 1 and 2 A for residues Tyr75 and Arg309 and very small shifts for the region of residues 42 to 44 from the symmetry-related subunit. Kinetic studies demonstrate that NADH inhibits the AMP activation of glycogen phosphorylase b. Crystallographic binding studies at 3.5 A resolution show that NADH binds to the same sites on the enzyme as AMP, i.e. the allosteric effector site N, which is close to the subunit-subunit interface, and the nucleoside inhibitor site I, which is some 12 A from the catalytic site. The conformations of NADH at the two sites are different but both conformations are "folded" so that the nicotinamide ring is close (approx. 6 A) to the adenine ring. These conformations are compared with those suggested from solution studies and with the extended conformations observed in the single crystal structure of NAD+ and for NAD bound to dehydrogenases. Possible mechanisms for NADH inhibition of phosphorylase activation are discussed.     

Effect of 3-phenylindole on lipophilic ion and carrier-mediated ion transport across bilayer lipid membranes

The physical effects of 3-phenylindole, an antimicrobial compound which interacts with phospholipids, on ion transport across phosphatidylcholine-cholesterol bilayers have been investigated using three lipophilic ions and one ion-carrier complex. It was found that 3-phenylindole increased membrane electrical conductance of positively charged membrane probes and decreased electrical conductance of negatively charged probes. The enhancement of conductance detected by nonactin-K+ complex and tetraphenylarsonium+ was several orders of magnitude, whereas the suppression of conductance due to tetraphenylborate- and dipicrylamine- was less than a factor of ten. Presence of 3-phenylindole in aqueous phase slightly decreased adsorption of tetraphenylborate- and dipicrylamine- at the membrane surface. From the voltage dependence of the steady-state conductance it was shown that 3-phenylindole induced kinetic limitation of membrane transport of potassium mediated by nonactin. No such limitation was found in the case of tetraphenylarsonium+ transport. These results are shown to be consistent with the present concept of ion diffusion in membranes and the assumption that 3-phenylindole decreases the electric potential in the membrane interior. The asymmetry of the effect of 3-phenylindole on the magnitude of conductance changes for positively and negatively charged membrane permeable ions is also discussed as a reflection of the discreteness of both the absorbed 3-phenylindole and lipid dipoles.