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T M Roberts

Publications and source records attributed to T M Roberts.

At least 199 records · Page 11Linked to original sources
PubMed1979

Synthesis of simian virus 40 t antigen in Escherichia coli.

Plasmids are constructed by using recombination in vitro according to Roberts, T.M., Kacich, R. & Ptashne, M. (1979) Proc. Natl. Acad. Sci. USA 76, 760-764 in which the t antigen gene of simian virus 40 is fused to a promoter of the Escherichia coli lac operon. In the fusions, transcription commences at the lac promoter, and, in some of the fusions, translation begins at the ATG initiator codon of the t gene. This translation is directed most efficiently by those plasmids in which the lac sequences abut the t gene such that a hybrid ribosome binding is encoded. In this case, the Shine-Dalgarno sequence is of lac origin but the ATG derives from the t gene. translation from this initiator codon is greatly decreased if the lac sequences are separated from the ATG by 17 base pairs and is abolished if the AT of this triplet is deleted. Cells bearing the productive fusions synthesize a 20,000-dalton protein with t antigenic determinants. This protein has an isoelectric point(s) indistinguishable from that of t antigen isolated from simian virus 40-transformed cells. Moreover, a partial sequence of the amino-terminal region of the bacterial product is that predicted for authentic t antigen. We conclude that these bacteria are for authentic t antigen. We conclude that these bacteria are producing a protein, the sequence of which is identical to that of authentic t antigen unfused to other polypeptides.

Amino Acid Sequence↗
PubMed1979

A general method for maximizing the expression of a cloned gene.

We present a method, utilizing a combination of restriction endonuclease cleavage and digestion with Escherichia coli exonuclease III and Aspergillus orizae nuclease S1, that allows us to position a restriction fragment bearing the promoter of the lacZ gene of E. coli at virtually any distance in front of any cloned gene. In particular, we have used this method to examine the effect on protein production of gene-promoter separation for the cro gene of phage lambda and to produce plasmids that, upon transformation into appropriate E. coli hosts, direct the synthesis of up to 190,000 cro protein monomers per cell.

Base Sequence↗
PubMed1979

Extensive gas in tissues of the forearm after horsebite.

A 44-year-old man sustained lacerations of the forearm as a result of a horsebite. His arm became swollen after primary closure of the wounds, and a roentgenogram showed gas in the tissues of the forearm. Streptococcus anginosus and S mutans were isolated from the wounds.

Adult↗
PubMed1979

Behavioral responses of Schistosoma mansoni miracidia in concentration gradients of snail-conditioned water.

Movement patterns of Schistosoma mansoni miracidia were examined in several concentrations and gradients of snail-conditioned water (SCW). Miracidia surrounded by uniform concentrations of SCW swam at the same speed and exhibited the same rate of turning (angular velocity) as did control miracidia swimming in spring water. However, miracidia in gradients of SCW exhibited a 3-fold increase in their angular velocity without altering their swimming speed. Miracidia ascending gradients of SCW did not increase their angular velocity and failed to orient to the gradient of the stimulant. In contrast, miracidia which encountered sufficiently abrupt decreases in SCW concentration, while descending the gradient, sharply increased their angular velocity. This behavior caused miracidia to remain in regions of high concentration of stimulant. The magnitude of decrease in SCW concentration needed to evoke this response depended on the absolute concentration of SCW. Thus, the miracidial response is a "boundary reaction", a form of chemoklinokinesis, and not a chemotaxis.

Animals↗
PubMed1978

A simple quantitative technique for testing behavioral responses of Schistosoma mansoni miracidia to chemicals.

We describe a new technique for testing responses of Schistosoma mansoni miracidia to chemicals. Miracidia in spring water were placed in a chamber shaped like the Greek letter phi. Small volumes of test chemicals were inoculated into one side of the chamber. After 30 sec a dam was inserted to bisect the chamber and the percentage of miracidia on the inoculated side was calculated. Reproducible quantitative results were obtained using the known miracidial stimulants, snail-conditioned water (Biomphalaria glabrata) and Mg2+; up to 80% of the miracidia were recovered on the inoculated side of the chamber. Other substances also stimulated miracidia: several inorganic cations, 4 neurotransmitters, 3 acetycholine antagonists, and 1 acetycholine agonist. Modifying the technique by testing stimulants in altered chemical "backgrounds" allowed us to test for inhibitors of miracidial responses. Assays of the Mg2+ content of several of the test solutions indicated that their stimulatory or inhibitory effects could not be ascribed to Mg2+ contamination. However, results obtained with neurotransmitters and drugs were not sufficiently consistent to implicate specific neurotransmitters in the mechanism by which miracidia detect and respond to stimulants in snail-conditioned water.

Acetylcholine↗
PubMed1977

Chemical attraction between adults of Nippostrongylus brasiliensis: description of the phenomenon and effects of host immunity.

Attraction between adults of Nippostrongylus brasiliensis was studied both in vivo and in vitro particularly with regard to the effects of host immunity on the behavior of the parasite. Most worms were found in clusters in the intestines of larval-infected rats but the number of isolated worms, particularly females, was greater in 14-day (immune) than in 7-day infected (nonimmune) hosts. Intubation of small numbers of normal adults into uninfected rats resulted in recovery of mostly aggregated worms unless infections consisted only of males. In contrast, immune-damaged worms exhibited little aggregation regardless of the sexes of worms instilled. Analysis of pairing between worms in vitro indicated that attraction occurred in the absence of host factors between all permutations of normal worms except male-male combinations. Pairing between damaged worms occurred only between males and females and not between worms of the same sex. Attraction to worm excretory and secretory products (ES) indicated that chemical factors mediated pairing. Normal female ES was attractive to both sexes whereas damaged female ES failed to attract either sex. ES from both normal and damaged males attracted females but not males thereby confirming the results of other experiments.

Ancylostomatoidea↗
PubMed1976

The blue-green alga agmenellum quadruplicatum contains covalently closed DNA circles.

This paper reports the first direct visualization of covalently closed, circular DNA from a blue-green alga. Agmenellum quadruplicatum lysates, fractionated on CsCl-ethidium bromide density gradients, yield a minor band of covalently closed DNA circles which we have analyzed by electron microscopy and agarose gel electrophoresis. The DNA consists of a number of a discrete classes of DNA circles ranging in molecular weight from 3 X 10(6) daltons to 65-80 X 10(6) daltons. The function of these circles is at present entirely unknown.

Centrifugation, Density Gradient↗
PubMed1974

Lead contamination around secondary smelters: estimation of dispersal and accumulation by humans.

A high rate of lead fallout around two secondary lead smelters originated mainly from episodal large-particulate emissions from low-level fugitive sources rather than from stack fumes. The lead content of dustfall, and consequently of soil, vegetation, and outdoor dust, decreased exponentially with distance from the two smelters. Between 13 and 30 percent of the children living in the contaminated areas had absorbed excessive amounts of lead (more than 40 micrograms per 100 milliliters of blood and more than 100 micrograms per gram of hair) as compared with less than 1 percent in a control group. A relationship between blood and hair was established which indicated that the absorption was fairly constant for most children examined. It seemned that the ingestion of contaminated dirt and dusts rather than "paint pica" was the major route of lead intake. Metabolic changes were found in most of 21 children selected from those with excessive lead absorption; 10 to 15 percent of this group showed subtle neurological dysfunctions and minor psychomotor abnormalities.

Adult↗