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J W Roberts

Publications and source records attributed to J W Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1982

Transcription terminates at lambda tR1 in three clusters.

Transcription of the rightward operon of bacteriophage lambda terminates in the presence of rho factor at a region known as tR1, located downstream of the structural gene for the lytic repressor cro. We demonstrate by nuclease Sl mapping that transcription termination at lambda tR1 occurs in vitro over a stretch of 60 nucleotides. End points of transcripts are clustered in three distinct regions, which we refer to as termination sites I, II, and III. Termination at site I is inhibited by L factor, whereas termination at sites II and III is not affected by L factor. The sensitivities of these sites to rho factor are in the order III greater than II greater than I. The cin-lcnc-l mutations abolish termination at site II but not at sites I and III; this result may explain the failure of these mutations to alleviate the phage requirement for N function for growth. Although possible stem-and-loop structures in the RNA transcript immediately upstream of each of the three termination sites can be found, no consistent correlation exists between the strengths of these stem-and-loop structures and the termination efficiencies of their respective sites.

Bacteriophage lambda↗
PubMed1982

Microtube coagulase test for detection of coagulase-positive staphylococci.

Studies were performed to determine the sensitivity and specificity of a new microtube method for the detection of coagulase production by Staphylococcus aureus. Rabbit plasma containing EDTA was added to and lyophilized in API microtubes. Two standard coagulase plasmas containing EDTA were used in the conventional macrotube test and served as a basis for comparison. No false-positive or false-negative reactions were encountered with the microtube system. With this system, 53% of the coagulase-positive strains tested were detected within 1 h after inoculation, 82% were detected after 2 h, 97% were detected after 3 h, and 99% were detected after 4 h. With the first conventional method, 45, 81, 96, and 98% of the positive strains were detected in 1, 2, 3, and 4 h, respectively, whereas with the second conventional method, only 6% of the positive strains were detected in 1 h, 24% in 2 h, 66% in 3 h, and 81% in 4 h. With the microtube method, 5 of the 139 coagulase-producing strains studied reverted to negative between 5 and 24 h after inoculation, whereas 9 reverted with the more rapid conventional method, and no reversions occurred with the second conventional method. All reversions involved strains which caused gelation of plasma within 1 h after inoculation. The data obtained showed that 99% of the coagulase-positive strains tested could be detected within 4 h by the microtube method. In addition, the microtube method offers a more convenient and economical format for the performance of the coagulase tube test.

Animals↗
PubMed1982

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Equipment and Supplies, Hospital↗
PubMed1981

Function of nucleoside triphosphate and polynucleotide in Escherichia coli recA protein-directed cleavage of phage lambda repressor.

Escherichia coli recA protein catalyzes a specific proteolytic cleavage of repressors in vitro when it is activated by interaction with a single-stranded polynucleotide and nucleoside triphosphate. The ATP analogue adenosine-5'-O-(3-thiotriphosphate) (ATP gamma S) satisfies the NTP requirement. We show here that despite its activity in repressor cleavage, ATP gamma S is hydrolyzed at a negligible rate by the recA protein DNA-dependent nucleoside triphosphatase activity. In the presence of DNA, ATP gamma S binds tightly to recA protein in a complex that can be detected because it is trapped by a nitrocellulose filter. One ATP gamma S molecule is bound per recA monomer. These results suggest that a ternary complex of recA protein, DNA, and nucleoside triphosphate is the species active in repressor cleavage. The activation of recA protein by small, defined oligonucleotides in place of DNA is described and characterized.

Adenosine Triphosphate↗
PubMed1981

Two mutations that alter the regulatory activity of E. coli recA protein.

The Escherichia coli recA gene product is both a direct participant and a central regulatory element in important processes of DNA repair, including one that is probably responsible for all radiation mutagenesis and some chemical mutagenesis. It has the direct function of catalysing pairing of single-stranded DNA to a homologous region in duplex DNA, a reaction thought to be fundamental to genetic recombination. This activity of recA protein probably contributes to DNA repair by promoting recombination between damaged DNA molecules. We have shown that recA protein also has a regulatory function, mediated by its ability to destroy repressors and possibly other proteins by proteolytic cleavage, leading to the induction of certain genes; these include recA itself, regulated by the lexA gene product, other genes probably involved in DNA repair, some of which are also regulated by the lexA gene product, and the early genes of temperate bacteriophages, which are regulated by their repressors, recA protein is activated to cleave repressors in vitro by interaction with ATP (or the ATP analogue ATP-gamma S) and a polynucleotide such as single-stranded DNA, probably the same interaction that initiates the strand-pairing reaction. We have proposed that recA protein is also activated to attack repressors in vivo when it interacts with single-stranded DNA; DNA-damaging treatments such as UV-ray irradiation would thereby invoke the recA-dependent functions of recombination, repair, mutagenesis and prophage induction. As further evidence that the proteolytic activity of recA protein is responsible for its regulatory function, we show here that the ability of two mutationally altered recA proteins to cleave phage lambda repressor correlates with the ability of the mutant cells to induce prophage.

Adenosine Triphosphatases↗
PubMed1981

Induction of SOS functions: regulation of proteolytic activity of E. coli RecA protein by interaction with DNA and nucleoside triphosphate.

Damage to cellular DNA or interruption of chromosomal DNA synthesis leads to induction of the SOS functions in E. coli. The immediate agent of induction is the RecA protein, which proteolytically cleaves and inactivates repressors, leading to induction of genes they control. RecA protein modified by tif mutations allows expression of SOS functions in the absence of inducing treatments. We show here that tif-mutant RecA protein is more efficient than wild-type RecA protein in interacting with DNA and nucleoside triphosphate. This result suggests that formation of a complex with DNA and nucleoside triphosphate is the critical event that activates RecA protein to destroy repressors after SOS-inducing treatments, and that damage to cellular DNA promotes this reaction by providing single-stranded DNA or active nucleoside triphosphate or both. Since dATP is the most effective nucleoside triphosphate in promoting repressor cleavage, we suggest that it is the natural cofactor of recA protein in vivo.

Adenosine Triphosphate↗
PubMed1981

Hepatic abscess due to Yersinia enterocolitica without bacteremia.

A 71-yr-old diabetic patient was evaluated because of right upper quadrant pain. He was found to have a large hepatic abscess secondary to Yersinia enterocolitica infection. He lacked clinical evidence of bacteremia or gastrointestinal infection. It is postulated that Yersinia enterocolitica reached the liver through the portal system from an inapparent intestinal infection. This is the first reported case of a liver abscess secondary to Yersinia enterocolitica without evidence of systemic infection.

Aged↗
PubMed1980

E. coli recA protein-directed cleavage of phage lambda repressor requires polynucleotide.

The recA protein mediates both genetic recombination and several cellular responses to DNA damage, including the induction of temperate bacteriophage. Indication of phage lambda results from proteolytic cleavage of lambda repressor directed by recA protein. We show here that this cleavage reaction requires both polynucleotide and ATP. We suggest that a stoichiometric complex of recA protein and DNA is active both to destroy repressors by proteolytic cleavage and to initiate pairing of this DNA to its homologous sequence in a DNA duplex ('strand invasion').

Adenosine Triphosphate↗