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It is suggested that there are three major determinants of vegetation—competition, stress and disturbance—and that each has invoked a distinct strategy on the part of the flowering plant. A method is described whereby it is possible to distinguish types of herbaceous vegetation by reference to the relative importance of the three strategies in the genotypes of the component species.

The genes for at least two Escherichia coli RNA polymerase subunits are contained in a single operon.

A new type of host defective Escherichia coli mutant, hd590, is described. T4+ infection of this mutant results in (1) an abnormally low rate of T4 DNA synthesis that is constant throughout the latent period; (2) relatively low amounts of specific late T4 proteins; (3) the production of empty T4 heads, but not of tails or tail fibres. Two types of T4 mutants, one in T4 gene 31 and the other near T4 gene 39, overcome the hd590 block.

IN previous papers it has been shown that the in vitro template activity of DNA1 and chromatin2 with DNA polymerase I of Escherichia coli is altered by the action of ionising radiation. These changes have been attributed1 to the formation of new binding sites on the DNA for the enzyme, some sites being active in the synthesis of DNA and others inactive. These new sites are associated with single-strand breaks in the DNA. By working under conditions either of enzyme excess or of excess of template it is possible to distinguish between newly formed active and inactive enzyme binding sites.

Chimaeras have been derived from aggregation of normal and dystrophic mouse embryos which had healthy muscles of almost totally dystrophic genotype, and diseased muscles of normal genotype. These results suggest that extramuscular factors must be implicated in muscular dystrophy.

The temperate bacteriophages P22 of Salmonella typhimurium and λ of Escherichia coli form viable hybrids in which the immunity, early control and DNA replication genes of P22 are substituted for the analogous λ genes. The specificity of the early control and DNA replication genes differs between P22 and λ; the immunity of the hybrid is identical with that of the lambdoid coliphage 21. Implications for the evolution of viruses are discussed.

Analysis of the interaction between mRNA codons and tRNA anticodons suggests a model for the evolution of the genetic code. Modification of the nucleic acid following the anticodon is at present essential in both eukaryotes and prokaryotes to ensure fidelity of translation of codons starting with A, and the amino acids which could be coded for before the evolution of the modifying enzymes can be deduced.

THE protein trypsin inhibitors are proteins which bind very strongly to trypsin, blocking its active site (Ki = 10−9 to 10−14 M) we have carried out a crystal structure analysis of the complex of soybean trypsin inhibitor (Kunitz) (STI), one of the largest inhibitors, with porcine trypsin. Huber and his colleagues have determined the structure of a complex of a small inhibitor, bovine pancreatic trypsin inhibitor (Kunitz) (PTI), with bovine trypsin1. These studies improve our understanding of the catalytic mechanism of trypsin, demonstrate that various trypsin inhibitors act in a similar way and provide insight into the development of strong, specific binding between protein molecules.

THE antimitotic action of (±)-1,2-bis (3,5-dioxopiperazin-1-yl) propane (ICRF 159) has been extensively studied in vivo in human1 and animal tumours2,3, but its mode of action at the cellular and biochemical level has not yet been elucidated. Although it reduces the rates of DNA, RNA and protein synthesis of cells in vitro4, it has also been shown to block the cell generation cycle in the post-DNA synthesis (G2) phase5,6. Tumours whose growth is halted contain many large multinucleate cells not seen in control tumours. An attempt has therefore been made to see if the morphological changes produced by the drug in cells grown in vitro could provide an indication of its intracellular site of action and point towards possible mechanisms of action. The cells used were non-synchronised cultures of non-transformed hamster fibroblasts (Nil 8 cells), HeLa cells and fibroblasts derived from a transplantable fibrosarcoma in Syrian hamsters (T17 cells). They were exposed to single daily doses of ICRF 159 for 3 d.

Amino acid sequences in elastin contain striking patterns. These are interpreted in terms of possible molecular conformations, and an ‘oiled coil’ model is proposed to explain the protein's elastic behaviour.

WE have recently described a mouse melanoma cell line which responds to melanocyte stimulating hormone (MSH) with dramatic increases in tyrosinase activity and melanin content, as well as changes in cellular morphology and growth characteristics1–3. The increase in pigmentation following exposure to MSH is shown in Fig. 1. Cyclic AMP or dibutyryl cyclic AMP may be substituted for MSH in eliciting these responses; consistent with other work suggesting that MSH acts through cyclic AMP in the control of pigmentation in vertebrates4–7. In our previous studies we used non-synchronised mouse melanoma cells grown in monolayer culture. Martin et al.8 have shown that synchronised mouse HTC cells respond to corticosteroids with increased tyrosine amino transferase synthesis in the late Gl and early S periods of the cell cycle; similarly, Buell and Fahey9 have shown, using a synchronised human lymphoid cell line, that immunoglobulins G and M are expressed in late Gl and S. We wished to investigate the effects of MSH on tyrosinase activity and endogenous cyclic AMP levels in synchronised cells to determine if there is a particular hormone-sensitive phase of the melanoma cell cycle. We report here that melanoma cells responded maximally to MSH with increased tyrosinase activity and cyclic AMP content during the G2 phase.

The interaction between echinomycin and circular DNA or sonicated rod-like DNA fragments shows that this antibiotic binds by a bifunctional mode of intercalation. Binding parameters for a variety of natural and synthetic DNAs vary widely, indicating that echinomycin interacts selectively with specific nucleotide sequences.

THE hazard to man of environmental contamination by certain metals is of considerable importance and in this context the organic and inorganic compounds of lead are the subject of much current interest. The clinical effects on the individual of accidental overexposure to lead are well known. What is perhaps not so widely realised, however, is that there is the possibility that high lead levels may be hazardous to the foetus of exposed parents. “Intoxication with lead” is often quoted as “reducing fertility and increasing the frequency of abortions and miscarriages” in man1–5, and some animal studies have shown6 that administration of lead salts may result in an increase in congenitally malformed offspring. These findings, the reported carcinogenicity of lead salts in rats7, and the earlier reports that salts of a variety of heavy metals induce aberrations in plant chromosomes8,9, have stimulated a number of in vitro and in vivo studies into the possible mutagenic effects of lead which have yielded conflicting results.

Geophysical data strongly indicate that stone assemblages, which include bifaces and cleavers, from East Africa, are at least a million years old. Since these artefacts seem to be much older than any of their known counterparts in Europe, the question of the date of man's expansion from the tropics into cool, temperate regions is raised for discussion.

THE adaptive strategy of sequestering cardiac glycosides from milkweed plants (Asclepiadaceae and Apocynaceae) has evolved in several taxa of insects1. Since these cardenolides elicit vomiting following ingestion, birds learn to avoid the insects on sight after one or more emetic experiences2. By a specific assay, we found a spectrum of cardenolide concentrations in adult monarch butterflies (Danaus plexippus L., Danainae) collected during the autumnal migration from four areas in eastern North America3. In this communication we compare Atlantic with Pacific Coast monarch populations and explore quantitative relationships between cardenolide concentrations and palatability spectra. The latter were measured by our blue jay (Cyanocitta cristata bromia Oberholser, Corvidae) emetic dose fifty (ED50) test4.

PROGRESS in somatic cell genetics now allows more rapid and precise localisation of genes within the human genome. A large number of mouse × human hybrid cell lines are available, permitting the investigator to choose, for phenotype assay, lines with a particular reduced human chromosome complement. An increasingly large number of hybrid lines carrying rearranged chromosomes are also becoming available for regional localisation studies. We have used such hybrid cell lines to assign a gene coding for galactokinase (EC 2.7.1.6) to human chromosome 17 and to further localise the gene to band 21–22 on the long arm of the chromosome. Results from this study have provided new information Regarding the functioning of the genes coding for the Leloir pathway enzymes in man1, and have revealed a relatively close and potentially useful linkage between the genes for galactokinase and for thymidine kinase (EC 2.7.1.21).

Two closely related polypeptides termed thymin I and II were isolated from bovine thymus by their effect in causing a delayed impairment of neuromuscular transmission in vivo. Purified thymin also induced bone marrow cells to develop the characteristics of intrathymic lymphocytes and it is probable that thymin is a lymphopoietic differentiating hormone of the thymus with secondary neuromuscular effects.

The ilv 1 gene of Saccharomyces cerevisiae contains functions associated with both structural and regulatory genes and therefore is termed a multifunctional gene. The ilv 1 gene product catalyses the first step in isoleucine biosynthesis and is involved in repression of the isoleucine-valine pathway. The intracistronic discrimination of the two functions is presented.

ENERGY-linked Ca2+ accumulation occurs in mitochondria isolated from different tissues and species (for reviews see refs 1 and 2). If the Ca2+ concentrations are kept relatively low, such accumulation does not lead to any apparent biochemical damage to the mitochondria, particularly to those processes associated with ATP synthesis. Once the concentration of Ca2+ in the incubation system approaches values of 100–150 nmol per mg protein, however, the ion induces imtochondrial swelling, release of the accumulated Ca2+ and total loss of acceptor control of respiration3–6. The latter situation is brought about through an increase in state IV respiration to a rate which approaches that of state III. Other events which occur include stimulation of ATPase activity, greatly diminished ADP-ATP exchange and 32Pi-ATP exchange activities and P/0 ratios4,6. All these events reach maximum at approximately identical concentrations of Ca2+ and so seem to reflect some common interaction of this ion at the intact (inner) membrane with which these energy-linked reactions are intimately associated.

The two regions of λ DNA to which the λ repressor binds (the operators) are shown to consist of multiple, non-identical repressor binding sites. The arrangement of these sites with respect to the adjacent controlled genes has been determined using a restriction endonuclease that cleaves each operator.

SINCE Swim and Parker1 and Hayflick and Moorhead2 documented the limited life span of diploid human fibroblasts in cell culture, many investigators have used these cells as possible models of cellular senescence. Most normal human fibroblasts exhibit marked cellular changes and eventually cease growth after fifty to seventy cell divisions. Hayflick3 and Martin et al.4 demonstrated an inverse relationship between the life span of cultured human diploid fibroblasts and the age of the donor. Furthermore, fibroblasts from children with premature ageing diseases have a markedly reduced potential for cell division4. Many investigators have studied human fibroblasts to determine whether their finite life span is related to ageing, and to determine the mechanism of ‘senescence’ in these cells5. There is no firm evidence, however, that fibroblast ‘ageing’ or limited fibroblast division potential is necessarily involved in the tissue and organ changes associated with ageing of individuals. Many types of cells which are obviously important in ageing of the whole organism undergo little or no division in adults (for example, neurones), and others which divide rapidly (for example, intestinal epithelium) have not been shown to behave as fibroblasts do, either in culture or in the organism.

THERE is an identifiable serotonin-containing neurone in each cerebral ganglion of the snail Helix pomatia1. Electrophysiological evidence suggests that each neurone sends a process into each cerebro–buccal connective2,3, and that monosynaptic connections are made in each buccal ganglion with other large identifiable neurones3. Because this neuronal system seems to offer a unique opportunity to study the proposed transmitter role of serotonin3,4, it is important to obtain direct information on the localisation and morphology of the presynaptic endings of the serotonin cell. This is not possible with dye5 or metal ion6 injection techniques, which do not seem to mark processes of the serotonin neurone at distances of more than a few millimetres from the neurone perikaryon.

MOST untransformed mammalian cells require an appropriate surface for survival and growth in vitro; this phenomenon has been termed anchorage dependence1. Glass, tissue culture plastics, fibrin clots and collagen surfaces have long been recognised as substrates able to support the attachment and growth of cells. Since the cell plasma membrane is separated from plastics substrates by a 450 A layer of electron opaque material2, the nature of the 450 A would appear to be more important in cell attachment than the chemical composition of the plastic. It is demonstrated here that cell attachment to collagen is mediated by a high molecular weight protein present in serum.

INTEREST in the infection of insects by parasites has been generated by the pathogenic potential of the parasite to the insect itself, or to a vertebrate host to which the parasite may be transmitted. For example, because of the effects of malaria on man, the relationships between Plasmodia and various mosquito species have received much attention1,2. An important part of the host-parasite relationship is the defence system of the host. In insects, phenoloxidase (o-diphenol: O2 oxidoreductase, EC 1.10.3.1.) has been suggested to be at least partially responsible for insect immunity and parasite resistance3–5.

Biochemical evidence suggests that the two tRNATyr1 genes of E. coli are transcribed together as a single precursor. A nuclease activity which cleaves incorrectly but specifically the tRNATyr precursor has been revealed.

In albino mammals, the absence of pigmentation in the eye is associated with abnormalities of the visual pathway and these result in a scrambled input to the visual centres of the brain. Recent research on Siamese cats, in which more than one pattern of abnormality has been found, shows that there are several ways in which the cortex can deal with the abnormal input, and is beginning to define the rules according to which the cortex selects its inputs.

WORKERS1–5 have reported IgG-precipitating antibodies against predominantly high molecular weight ruminant immunoglobulins to be present in the sera of certain patients with IgA deficiencies. The most frequently identified antigen is bovine IgM but we have also found a high frequency of precipitating antibodies to bovine associated mucoprotein (BAMP) (Table 1). Immunochemical studies have demonstrated that the antibodies to these two proteins are entirely distinct and that antibodies to BAMP in human sera can only precipitate with a fraction of the antigenic determinants detected by antisera raised in rabbits against BAMP.

A 3.5 A resolution electron density map of yeast phosphoglycerate mutase has been calculated which shows that much of the tertiary structure of this enzyme resembles that found in a number of nucleotide binding enzymes although the mutase itself has no known nucleotide binding requirement.

FGF, a polypeptide found in brain and pituitary, provokes the initiation of DNA synthesis by resting ST3 cells. When glucocorticoids are present FGF stimulates DNA synthesis as effectively as serum.

THE usual pattern of chromosome segregation in interspecific human×mouse somatic cell hybrids is retention of mouse and loss of human chromosomes1. In attempts to generate hybrid strains expressing differentiated functions, we have fused an actively dividing human cell line with freshly dissociated, highly differentiated cells from the mouse embryonic nervous system. The majority of the resulting hybrid strains retain human while losing mouse chromosomes and isozymes and thus provide a new class of hybrid cell for analysis of gene linkage and regulation.

THE rate of protein synthesis in eukaryotic cells can change rapidly as a result of translational control such as the inhibition of protein synthesis during mitosis1 or starvation2–4. Under these conditions a reversible inhibition of the initiation step of protein synthesis decreases the rate at which ribosomes become attached to messenger RNA. The continuing runoff of ribosomes from messenger during protein chain elongation and termination depletes the percentage of the total ribosomes which are in the form of polysomes and are synthesising protein.

A distinct structural response in disk membranes from frog retinal rod outer segments was found directly proportional to exposure to light. Translocation of rhodopsin from the intradisk hydrophilic surface to the internal hydrophobic phase of the membrane was observed.

Rhodopsin undergoes rapid lateral diffusion in the disk membranes of isolated frog and mudpuppy rods. The rate of lateral diffusion is consistent with the rapid rotational diffusion of rhodopsin: both indicate the disk membrane is highly fluid with a viscosity of ∼1P.

OF the four subunits of Qβ replicase, I, III and IV are bacterial proteins and II is coded for by the phage genome1,2. Among host-derived subunits, I is identified as factor i, a protein which controls cistron-specific translation in Escherichia coli3,4, and III and IV are identified as protein synthesis elongation factors, EFTu and EFTs (ref. 5), respectively.

RIBONUCLEIC acid-dependent RNA polymerase (replicase) was first isolated from Escherichia coli infected with RNA bacteriophage Q β which has specific template requirements1. Such an enzyme has been described in tumour cells and several types of mammalian cells infected with RNA viruses2–5.

Murine neuroblastoma cells in serum-free medium undergo correlative morphological and serological differentiation. The antigens specific to the differentiated cells are found in large quantities in mouse brain.

Rectification of gene copies by replication of a master copy cannot occur at every meiosis, or substantial DNA synthesis would result. If replication is the method of rectification, the process is likely to be restricted, in any one meiotic cell, to the genes that have undergone recombination.

Studies on a rat sarcoma link plasma membrane alterations to the activity of DNA-directed RNA polymerase II.

SEXUAL differentiation of gonadotrophin secretion in the rat is known to occur during the early postnatal period under the action of testicular androgens1,2. Animals of either sex if exposed to androgen during this critical period develop the typical male pattern of gonadotrophin secretion after puberty with failure of ovulation, small polyfollicular ovaries lacking corpora lutea and a constant cornified vaginal epithelium. Several studies have localised this effect to the brain3,4 and more particularly to the anterior hypothalamus5, but very little is yet known of the mechanism of this effect.

As in other species of poeciliid fish, male Xiphophorus variatus (Pisces, Poeciliidae) virtually cease growth at maturity. The size of an adult male, then, is determined by its average growth rate before it reaches maturity and the age at which this happens. The latter factor is under social control in this species. When I raised juvenile males in groups, they usually started to mature in sequence, largest first, and subsequently maturing males did not usually reach maturity until they were longer than all previously matured males. As a result, the juvenile size order was negatively correlated with adult size order. When the fish in a group were isolated from one another such patterns disappeared indicating that some degree of social interaction was necessary for their maintenance1.

REMARKABLE changes in the levels and properties of ribonuclease (RNase) occur following the inoculation of a susceptible variety of flax (Linum usitatissimum L., var. Bison) with flax rust uredospores (Melampsora lini (Ehrenb.) Lev, race 3)1. The increase in RNase activity occurs in two distinct phases; an early phase between 2 to 4 d after inoculation (early RNase) and a later phase, beginning 5 d after inoculation (late RNase). These increases in RNase activity are accompanied by substantial changes in the properties of the enzyme including thermal stability, diethyl-pyrocarbonate-sensitivity and substrate preference1. Further studies (A. K. C., M. S., and L. A. S., unpublished) have revealed that these changes in the properties of RNase are due, at least in part, to the formation of new RNase molecules. These have kinetic and catalytic properties that are quite distinct from both of those ‘host’ RNase from healthy flax cotyledons and ‘rust’ RNase from flax rust uredospores or from rust mycelium grown axenically in a chemically defined medium. That changes in late RNase activity are specifically elicited by compatible host-parasite interactions is indicated by the appearance of late RNase which is not detectable in a resistant variety of flax (Bombay) inoculated with race 3 of Melampsora lini1. Furthermore, the characteristic bimodal increase in RNase activity and the accompanying changes in various properties of the enzyme have been found in a number of other rust-infected plants including pine and Ribes (A. E. Harvey, A. K. C., M. S. and L. A. S., unpublished), and mechanical injury of the healthy host tissues causes a significant increase in the level of RNase. The enzyme remains strictly ‘host-type’, however, no change in its physical or catalytic properties being detectable (ref. 1 and A. E. Harvey, A. K. C., M. S., and L. A. S., unpublished). Here we describe the effect of inoculation with uredospores of three races (56, 56A and Australian race 126 ANZ-6, 7) of wheat stem rust (Puccinia graminis (Pers.) f. sp. tritici Eriks. and E. Henn.) in causing quantitative and qualitative changes in the RNase activity of paired, near-isogenic lines of wheat (Triticum aestivum L.) derived from the variety Chinese Spring and carrying the alleles Sr6 and sr6 (refs 2 and 3), respectively. Both lines give susceptible reactions (infection type 4 (ref. 4)) with race 56A, independent of temperature. The homozygous recessive, sr6, imparts susceptibility (infection type 4) to races 56 and 126 ANZ-6, 7. The dominant allele, Sr6, confers a temperature sensitive reaction to these races; resistance is expressed (infection type 0 (ref. 4)) at 19 to 21° C but breaks down (infection type 4) at higher temperatures (25 to 26° C). A few intercellular hyphae are produced at each infection site at 19 to 21° C. These survive for several days and resume growth when infected plants are transferred to 25 to 26° C; but, in our experience, the longer infected plants are held at 19 to 21° C before transfer, the smaller are the number and size of the sporulating pustules to be developed.

A new theory is proposed to explain the synthesis of the 5′ ends of linear DNA molecules. It suggests that chromosome ends consist of palindromic base sequences. These can form self-complementary hairpin loops, which can be converted by DNA ligase, a specific endonuclease, and DNA polymerase, into completely replicated ends.

RECENT evidence suggests that the structural genes of some transfer RNA molecules are clustered in groups of two or three on the Escherichia coli chromosome1–5. The arrangement of tRNA and spacer sequences for two such tRNA clusters have been described6–8. The pattern of transcription of tRNA genes in clusters is not known although the formation of larger precursors in tRNA biosynthesis has been reported9,10. In vitro transcription of tRNA1Tyr gene carried by ϕ80psu3+ phage DNA by purified RNA polymerase was shown to result in the formation of pre-tRNATyr molecules bigger in size than mature tRNA11. In the present communication we describe the transcription of a tRNA gene cluster (tRNA2Gly(su+36), tRNA2Tyr, tRNA3Thr) carried by the DNA of transducing phage λh80cI857S−t68dglyTsu+36tyrTthrT (abbreviated λh80T) recently isolated by Squires et al.5. In vitro transcription of this phage DNA by purified RNA polymerase is shown to produce pre-tRNA molecules of a molecular size consistent with the model of a polycistronic precursor.

STUDIES on Rous sarcoma virus (RSV), murine leukaemia virus (MuLV) and mammary tumour virus (MTV) systems have shown that at least parts of viral genomes are present in multiple copies in the natural host DNA. RSV-specific nucleotide sequences have been detected in various chick cells, including Rous sarcomas and embryos with or without RSV gs antigens and chick helper factor1,2. Similarly, normal and virus-transformed mouse and rat cells contained equivalent amounts of MuLV-specific DNA sequences3. MTV-specific DNA genomes have been detected in equal numbers in mouse strains with both high and low incidences of mammary tumours4. In addition, induction of leukaemia viruses from apparently uninfected mouse and chicken cells indicates that complete, ‘endogenous’ viral genomes are present in these cells5–8. But the integration of ‘exogenous’ viral genomes, upon infection with an oncogenic RNA virus, cannot be proved in an homologous system because of the lack of specific markers which could distinguish between exogenous and endogenous MuLV genes. Actual integration was demonstrated in the case of some heterologous systems, upon infection of duck and of mouse cells with RSV9.

Bacillus subtilis infected with bacteriophage PBS2 contains a new rifampicin-resistant RNA polymerase that is apparently composed of four different polypeptides.

LYMPHOCYTES can be activated in vitro by a variety of so-called polyclonal stimulants or mitogens (reviewed in refs 1, 2 and 3). These responses characteristically involve a larger proportion of cells than observed with antigen as the eliciting ligand, and the initiating events are widely believed to be independent of any immunogenicity possessed by the stimulant. These features of polyclonal responses provide the rationale for the use of such systems both as a model for the study of activation processes in lymphocytes2 and clinically for the assessment of proliferative potential of blood-borne lymphocytes4.

VARIOUS lymphocyte surface receptors can be redistributed after cross linkage by external ligands, leading to the formation of patches and caps1. At 21° C and 37° C concanavalin A (con A) in concentrations greater than 5 µg ml−1 inhibits patch and subsequent cap formation induced by anti-immunoglobulin and other reagents2,3. Con A can also induce cap formation by its own receptors under certain conditions, notably after binding at 4° C3,4. Thus con A has two antagonistic activities in modulating lymphocyte surface receptor distribution and their expression depends on the conditions of incubation. We now report results suggesting that colchicine-binding proteins5 (possibly those of the microtubules) are important in the modulation of cell surface mobility. In addition, we have found that alterations of pH affect the ability of lymphocytes to form patches and caps.

THE search for RNA-containing human breast cancer viruses has been helped by the discovery of several biochemical and biophysical characteristics of the oncornavirus group1–4. Although these properties may not be unique to oncornaviruses5, they provide biological reagents for more discriminating tests6–8 to establish species of origin, natural history and virus taxonomy for candidate viruses exhibiting these properties.

THE membranes of lymphoid cells from tumours induced by oncornaviruses are antigenically altered. The new surface antigen(s) are readily recognised by isologous (histocompatible) hosts which mount both cellular and humoral immune responses1,2. It is essential to know whether or not antigens induced by the various strains of murine leukaemia viruses (MuLV) are cross-reacting immunologically.

The duplicated genes coding for tRNATyrI have been isolated using site-specific nucleases and gel electrophoresis. An unduplicated sequence of 4–120 base pairs separates the two genes. Specific DNA fragments can be obtained in sizes appropriate for both functional and structural analysis of the tRNATyrI region.