The presence and binding characteristics of calmodulin in microsomal preparations enriched in sarcoplasmic reticulum from rabbit skeletal muscle

ATP-dependent oxalate facilitated calcium transport in sarcoplasmic reticulum (SR) preparations obtained from rabbit vastus lateralis muscle (fast skeletal muscle; F_sr) and soleus (slow skeletal muscle; S_sr) was determined. Addition of exogenous calmodulin did not stimulate calcium transport in either F_sr or S_sr preparations. F_sr and S_sr previously washed in 1 mM EGTA demonstrated a reduced capacity to transport Ca²⁺; the exogenous addition of calmodulin (0.24 μM) under these conditions, did not restore uptake activity but significantly decreased the steady-state level of Ca²⁺ uptake. Extracts of skeletal SR prepared by treatment with 0.2 mM EDTA and boiling produced significantly more stimulation of red cell Ca²⁺ATPase activity than extracts prepared by boiling alone. This stimulation of red cell Ca²⁺-ATPase was inhibited to a significant extent by $\text{48}\text{80}$, a known anti-calmodulin agent. Radioimmunoassay revealed that extracts prepared by boiling or EDTA-treatment followed by boiling contained considerable amounts of calmodulin. Washing with 1 mM EGTA, though, did not release any calmodulin from SR. These studies reveal that calmodulin is present in both F_sr and S_sr and can only be removed by harsh treatments. The role of calmodulin in skeletal muscle Ca²⁺-transport remains to be determined.     

A kinetic model for bacterial transfection: the lambda DNA system.

A kinetic model describing the binding and uptake of free lambda phage DNA by the bacterium Escherichia coli is presented. The model is based on the assumption that adsorbed ‘helper’ phage particles serve as functional sites to which the lambda DNA specifically binds. When applied to experimental data, the model describes the reaction between cells and DNA as a rapid binding of DNA to helper phage attachment sites, followed by a slow, irreversible incorporation of bound DNA into the cells. Features of the model include a time-dependent exponential decay of functional sites required for DNA uptake and a minimum time for irreversibly bound DNA to enter the cell. We suggest that this model may be useful in studying processes involved in the active transport of DNA across a permeability barrier.     

Computer simulation of cellular movements: cell-sorting, cellular migration through a mass of cells and contact inhibition

The motility rules for cellular movement proposed earlier by Goel &; Rogers for engulfment of two or more intact embryonic tissues have been used to simulate on a computer the phenomena of cell-sorting, migration of individual cells through a mass of cells and contact inhibition of overlapping. These simulations in the most part are found to be consistent with the observations with real cells.     

Folding of two large nucleotide chains

We have already described the FOLD-A code designed for folding mRNA's and single stranded DNA molecules (Nussinov & Pieczenik, 1984). In this paper we describe its application to two long polynucleotide chains: the A protein gene of the MS2 RNA and the whole genome of the phi X 174 phage. The folded form of the single stranded DNA of the phi X 174 is a six armed star with the origin of replication in its center.     

Bile acids. XL. Methyl 3beta, 7beta-dihydroxy-5alpha-cholanate. An example of dehydrogenation with Raney nickel

The bile acid derived from hydrogenolysis of methyl 6-oxo-3α, 7β-dihydroxy-5α-cholanate-6-ethylenethioketal with Raney nickel has been shown to be 3β, 7β-dihydroxy-5α-cholanic acid (VI). On extended reflux with Raney nickel the original C-3 hydroxyl group is dehydrogenated and the 3-oxo-derivative reduced principally to the equatorial 3β-o1. The positions and configurations of the hydroxyl groups were determined by reduction of the derived monohydroxy mono-oxo derivatives to the known monohydroxy acids. The materials (VI) has been synthesized from 3β-hydroxy-7-oxo-5α-cholanic acid by reduction with sodium and alcohol. Physical properties support the assigned structure.     

Community structure and abundance of insects in response to early‐season aphid infestation in wild cabbage populations

1. Changes in the arthropod community structure can be attributed to differences in constitutively expressed plant traits or those that change depending on environmental conditions such as herbivory. Early‐season herbivory may have community‐wide effects on successive insect colonisation of host plants and the identity of the initially inducing insect may determine the direction and strength of the effects on the dynamics and composition of the associated insect community. 2. Previous studies have addressed the effect of early infestation with a chewing herbivore. In the present study, the effect of early infestation was investigated with a phloem‐feeding aphid [Brevicoryne brassicae L. (Hemiptera, Aphididae)] on the insect community associated with three wild cabbage (Brassica oleracea L.) populations, which are known to differ in defence chemistry, throughout the season in field experiments. 3. Aphid infestation had asymmetric effects on the associated insect community and only influenced the abundance of the natural enemies of aphids, but not that of chewing herbivores and their natural enemies. The effect size of aphid infestation further depended on the cabbage population. 4. Aphid feeding has been previously reported to promote host‐plant quality for chewing herbivores, which has been attributed to antagonism between the two major defence signalling pathways controlled by the hormones salicylic acid (SA) and jasmonic acid (JA), respectively. Our results show no effects of early infestation by aphids on chewing herbivores, suggesting the absence of long‐term JA–SA antagonism. 5. Investigating the effects of the identity of an early‐season coloniser and genotypic variation among plant populations on insect community dynamics are important in understanding insect–plant community ecology.     

Control of Liriomyza langei on chrysanthemum by Diglyphus isaea produced with a standard or modified parasitoid rearing technique

Abstract: Overproduction of male parasitoids during mass rearing will increase costs for biological control because wasp shipments contain fewer females and only females kill hosts directly. We have developed a rearing technique capable of significantly reducing male‐biased sex ratios in Diglyphus isaea (Walker) (Hym., Eulophidae), a commercially reared parasitoid of agromyzid leafminers. In this study, we examined the effect of rearing technique on the efficacy of D. isaea for biological control of Liriomyza langei Frick (Dip., Agromyzidae) on chrysanthemum, Dendranthema grandiflora Tzvelev var. ‘Miramar’. We produced D. isaea on mixtures of small and large hosts (our modified technique) or on only large hosts (simulating commercial mass‐rearing) and compared: (1) control of L. langei with D. isaea produced by the two rearing techniques, and (2) damage and yield of unprotected and protected plants. The two rearing techniques produced similar numbers of waSPS per rearing cohort, but the ‘modified’ technique reduced the proportion of males by approximately 13%. The two techniques also produced females of similar size, but the ‘modified’ technique produced smaller males. In greenhouse trials simulating leafminer infestations of potted chrysanthemums during commercial production, we found no significant differences between the levels of control obtained by releasing identical numbers and sex ratios of adult waSPS produced by either rearing technique. Mine counts on plants protected by waSPS of either rearing history were similar and around 30–70% less than unprotected plants during most of the 11‐week crop cycle. At crop harvest, more than half of the foliage on protected plants was undamaged compared with <10% on unprotected crops. Damage to the flower stems of protected plants was relatively light in the top half of the canopy compared with the bottom half. Protected plants were around 10–15% taller and produced twice as many flower buds compared with unprotected plants. Our ‘modified’ rearing technique can reduce overproduction of males in D. isaea with no compromise in biological control efficacy. Adoption of our rearing technique by commercial insectaries could reduce implementation costs for not only D. isaea but also other parasitoids that show host‐size‐dependent sex allocation.     

Simple derivation of the function of genetic information and correction of the proof

The problem of predicting time to extinction in stochastics population models is approached in two ways. First, a finite Markov chain approximation is used to give the distribution of time to extinction and shown to predict simulation results accurately. Second, an approximate numerical integration technique is found to give good relative predictions of persistence using much less computer time. The relevance of the two approaches to real problems is discussed.