10 nm RecA protein filaments formed in the presence of Mg2+ and ATP gamma S may contain RNA

Summary Filaments formed by the polymerization of RecA protein along DNA in the presence of Mg²⁺ and adenosine 5-0-(3-thiotriphosphate) (ATPS) are seen by electron microscopy to have a 10 nm diameter with a 9 nm helical repeat. When certain preparations of apparently pure RecA protein are incubated with Mg²⁺ and ATPS in the absence of nucleic acid for extended times, very long filaments with the same 10 nm diameter and 9 nm axial repeat are seen. We show here that these long 10 nm filaments can contain RNA which is present as a contaminant of the RecA protein and poly(A) which is synthesized during the incubations by an activity that is apparently polynucleotide phosphorylase. RecA protein purified by a procedure developed in this laboratory did not contain RNA and did not form these very long 10 nm filaments. However, when exogenous RNA was added to this protein, 10 nm filament formation was observed.     

The giant (gt) mutants of Drosophila melanogaster alter DNA metabolism

Summary Abnormalities in DNA metabolism have been found in third-instar females of Drosophila melanogaster that are heteroallelic or homoallelic for X-chromosomal giant (gt) mutations. Analysis of DNA metabolism in larval brain ganglia was carried out using alkaline sucrose gradient centrifugation, incorporation assays and a neutral filter elution assay. These analyses show that gt stocks synthesize DNA of a reduced molecular weight, have an unusually high frequency of spontaneous single and doublestrand breaks, and exhibit a reduction in the normal inhibition of DNA synthesis following treatment with UV and the carcinogen AAAF. These phenomena are not associated with a defect in the repair of X-ray induced DNA breaks nor are they accompanied by any alterations in chromosome stability. Analysis of homozygous 1(2)gl larvae also reveal that these phenomena are specific to the gt locus and are thus not attributable solely to an extended developmental program. These findings strengthen the suggestion that the genetic instability associated with gt is related to perturbations in chromosome metabolism (Green 1982).Abbreviations used UV ultraviolet radiation-principal wavelength 313 nm - AAAF N-acetoxy-2-acetylaminofluorene     

A root observation and sampling chamber (rhizotron) for pot studies

Summary A plant root observation chamber (rhizotron) was designed to examine soil-grown roots under a stereomicroscope and to sample roots and soil during the growth period of a pot study. The mini-rhizotrons are inexpensive to construct and are suitable for replicated, multitreatment experiments. Illustrative data on root hair and lateral development are presented for seedlings of four crop species.Vermont Agric. Exp. Stn. Journal Article No 572.     

Two-dimensional nuclear Overhauser enhancement investigation of the solution structure and dynamics of the DNA octamer [d(GGTATACC)]2

The resonances of nearly all 70 of the non-exchangeable protons of the duplex [d(GGTATACC)]2 in aqueous solution are assigned by proton two-dimensional nuclear Overhauser enhancement (2D NOE) spectra obtained in pure absorption phase at 500 MHz. Experimental and theoretical 2D NOE spectra are compared at each mixing time (100, 175, 250 and 400 ms) using two B-DNA structures: a standard B-form and an energy-minimized form. The GG and CC ends of the octamer duplex are well represented by the regular B-DNA structure. But large discrepancies from these models are observed for the 'TATA' box. All 2D NOE data are consistent with nanosecond correlation times, as indicated by non-selective proton spin-lattice relaxation times, but small variations in the correlation time are observed, suggesting that there are some local differences in mobility within the octamer duplex structure in solution.     

Export of species to islands from sources of differing maturity

Export of species from sources (epicenters) of differing ages and complexities was examined using laboratory microcosms. Polyurethane foam (PF) artificial substrates were colonized by protozoans for different time periods in a small pond. Substrates were returned to the laboratory and used as epicenters for protozoan colonization of barren PF islands in initially sterile microcosms. Islands were exposed to epicenters for either 24 h or continuously for 28 d. Islands from pairs of microcosms exposed to epicenters of identical ages were sampled on 1, 3, 7, 14, 21, 28 and 46 d after initial epicenter exposure. Colonization parameters were estimated by fitting numbers of colonizing species to the MacArthur-Wilson equilibrium model. Islands exposed continuously to epicenters were colonized by significantly more species than those exposed for only 24 h. Islands exposed to immature, species poor epicenters were colonized by a greater proportion of the source community than those exposed to more mature, species rich epicenters. All islands were depauperate compared to epicenters except those exposed to the most immature (1 d old) epicenter. Colonization continued at a reduced rate in spite of the absence of the epicenter. Results from communities with rapid species turnover and rapidly reproducing species suggest that the continuous presence of a species source is less important for colonization of a new habitat. Dispersal of potential colonists occurs rapidly in these communities. Less mature communities dominated by pioneer forms are more effective at producing colonists than more mature communities.     

A critical scanning electron microscope study of the scolex of Bothriocephalus acheilognathi Yamaguti, 1934, with a review of the taxonomic history of the genus Bothriocephalus parasitizing cyprinid fishes

Summary Bothriocephalus specimens from one Ctenopharyngodon idella (O+) were fixed using three different techniques and the scolex morphology was examined using scanning electron microscopy. The scolices were compared with figures of the five species of Bothriocephalus and one species of Schyzocotyle previously described from cyprinid fishes. The taxonomic history of the Bothriocephalus species parasitizing cyprinid fish is reviewed. It is concluded that there is only one Bothriocephalus species parasitizing cyprinid fishes, and that continued use should be made of the name B. acheilognathi Yamaguti, 1934. ac]19840326     

Rationalization of some genetic anticodonic assignments

The genetic code appears to be a logic matrix in which, generally speaking, there is a correlation between the hydrophobicities of amino acids and their anticodonic nucleotides. There are several exceptions to this generality, however, and using previous data on hydrophobicity and binding constants, coupled with new data on reaction rates, we rationalize several of the anticodonic assignments.     

Analysis of the community structure of yeasts associated with the decaying stems of cactus. III.Stenocereus thurberi

Yeast communities in necroses of organpipe cactus (Stenocereus thurberi) were surveyed at 3 localities in Arizona. Quantitative analysis of random samples allows comparisons of the types and numbers of yeasts at 3 levels: within plants, between plants within a locality, and between localities. The analysis shows that the major source of variability is between plants. This pattern is identical with the pattern shown by agria cactus (Stenocereus gummosus) and is thought to be due to sampling different successional stages. No significant differences in estimates of the effective number of yeast species (ENS) in agria and organpipe samples were found. Comparisons of agria, organpipe, and prickly pear (Opuntia) cacti support the hypothesis that cactus chemistry is an important determinant of the yeast community structure which, in turn, is an important determinant of the diversity ofDrosophila species which utilize necrotic cacti as feeding and breeding substrates.     

Age and growth of a colonizing minnow,Barbus anoplus,in a man-made lake in South Africa

Synopsis Aspects of the life history of Barbus anoplus were studied in Lake le Roux, a turbid man-made lake on the Orange River, South Africa. This minnow underwent a population explosion and successfully colonized the shoreline of the newly-formed lake during the early phases of reservoir filling. Male and female B. anoplus reach sexual maturity in one year at about 40 mm fork length. They have a multiple spawning habit with the first spawning in November–January and the second in February–March. The growth of the two resulting cohorts is discussed. It is proposed that the offspring from the second spawning not only acts as a ‘back-up’ but is capable of prolonging the life of that year-class into an additional reproductive season. Most of the minnows die after their second summer, but more offspring from the second spawning, especially females, live into a third summer. Females attain a larger maximum size (73 mm FL) and age (3–4 years) than males (60 mm FL, 2–3 years). B. anoplus is small and short-lived with a high seasonal reproductive potential, which is in contrast to the larger Barbus species in the Orange River system. These life-history traits enable the species to colonize and successfully inhabit unstable environments and probably account for its widespread distribution.