AvaI and BsoBI restriction endonucleases are isoschizomers which recognize the symmetric sequence 5'CYCGRG3' and cleave between the first C and second Y to generate a four-base 5' extension. The AvaI restriction endonuclease gene (avaIR) and methylase gene (avaIM) were cloned into Escherichia coli by the methylase selection method. The BsoBI restriction endonuclease gene (bsoBIR) and part of the BsoBI methylase gene (bsoBIM) were cloned by the "endo-blue" method (SOS induction assay), and the remainder of bsoBIM was cloned by inverse PCR. The nucleotide sequences of the two restriction-modification (RM) systems were determined. Comparisons of the predicted amino acid sequences indicated that AvaI and BsoBI endonucleases share 55% identity, whereas the two methylases share 41% identity. Although the two systems show similarity in protein sequence, their gene organization differs. The avaIM gene precedes avaIR in the AvaI RM system, while the bsoBI R gene is located upstream of bsoBI M in the BsoBI RM system. Both AvaI and BsoBI methylases contain motifs conserved among the N4 cytosine methylases.

Amino Acid Sequence↗

PubMed1996

Protein splicing involving the Saccharomyces cerevisiae VMA intein. The steps in the splicing pathway, side reactions leading to protein cleavage, and establishment of an in vitro splicing system.

Protein splicing involves the excision of an internal protein segment, the intein, from a precursor protein and the concomitant ligation of the flanking N- and C-terminal regions. It occurs in mesophilic bacteria, yeast, and thermophilic archaea. The ability to control protein splicing of a thermophilic intein by temperature and pH in a foreign protein context facilitated the study of the mechanism of protein splicing in thermophiles. On the other hand, no direct studies have been done on the mechanism of protein splicing in mesophiles. We examined the splicing of a chimeric protein containing the intein of the vacuolar ATPase subunit (VMA) of Saccharomyces cerevisiae that involves cysteines rather than serines at the reaction center. The steps in the splicing process were deduced by analyzing intermediates and side products that accumulated as a result of amino acid substitutions and were found to be analogous to those occurring in thermophiles. Moreover, appropriate amino acid replacements allowed us to develop the first mesophilic in vitro protein splicing system as well as strategies for modulating the rate of protein splicing and for converting the splicing reaction to an efficient protein cleavage reaction at either splice junction.

Amino Acid Sequence↗

PubMed1996

Activation of glycosylasparaginase. Formation of active N-terminal threonine by intramolecular autoproteolysis.

The activation mechanism of glycosylasparaginase of Flavobacterium meningosepticum has been analyzed by site-directed mutagenesis and activation of purified precursors in vitro. Mutation of Thr-152 to Ser or Cys leads to gene products that are not activated in vivo but are activated in vitro because processing of the mutant precursors is inhibited by certain amino acids in the cell. Kinetic studies reveal that activation is an intramolecular autoproteolytic process. The involvement of His-150 and Thr/Ser/Cys-152 in activation suggests that autoproteolysis resembles proteolysis by serine/cysteine proteases. Multiple functions of the highly conserved active threonine residue are implicated.

Amino Acid Sequence↗

PubMed1994

Expression, purification, and crystallization of restriction endonuclease PvuII with DNA containing its recognition site.

We have overexpressed the type II restriction endonuclease PvuII (R-PvuII) in E. coli, prepared large amounts of the homogeneous enzyme, and crystallized it with an oligonucleotide carrying a PvuII recognition site. The cocrystals are orthorhombic space group P2(1)2(1)2(1) with cell constants a = 95.8 A, b = 86.3 A, c = 48.5 A, and diffract X-rays to at least 2.7 A. There is a complex of two protein subunits and one oligonucleotide duplex in the asymmetric unit.

Base Sequence↗

PubMed1992

Intervening sequences in an Archaea DNA polymerase gene.

The DNA polymerase gene from the Archaea Thermococcus litoralis has been cloned and expressed in Escherichia coli. It is split by two intervening sequences (IVSs) that form one continuous open reading frame with the three polymerase exons. To our knowledge, neither IVS is similar to previously described introns. However, the deduced amino acid sequences of both IVSs are similar to open reading frames present in mobile group I introns. The second IVS (IVS2) encodes an endonuclease, I-Tli I, that cleaves at the exon 2-exon 3 junction after IVS2 has been deleted. IVS2 self-splices in E. coli to yield active polymerase, but processing is abolished if the IVS2 reading frame is disrupted. Silent changes in the DNA sequence at the exon 2-IVS2 junction that maintain the original protein sequence do not inhibit splicing. These data suggest that protein rather than mRNA splicing may be responsible for production of the mature polymerase.

Amino Acid Sequence↗

PubMed1992

Phenylethylamine and piperidine alkaloids in aloe species.

Of the approximately 300 species of ALOE (Liliaceae) native to Africa and Arabia, leaf extracts of 224 species have been examined chromatographically for alkaloids using ninhydrin, Dragendorff's reagent, nitroprusside, and iodoplatinate as revealing agents. From these, 48 (21%) species contained compounds giving a strong colorimetric reaction with at least one of these reagents. Tyramine derivatives were identified in 18 species and piperidine derivatives in a further 6 species. The other coloured zones remain unidentified but often appeared to represent common amino acids. Some taxonomic correlations are suggested. The presence of the toxic hemlock alkaloids in aloes readily available for potential medicinal use by local inhabitants sounds a note of caution against the unthinking use of these otherwise useful plants.

Journal Article↗

PubMed1991

Nomenclature relating to restriction of modified DNA in Escherichia coli.

At least three restriction systems that attack DNA containing naturally modified bases have been found in common Escherichia coli K-12 strains. These systems are McrA, McrBC, and Mrr. A brief summary of the genetic and phenotypic properties so far observed in laboratory strains is set forth, together with a proposed nomenclature for describing these properties.

Alleles↗

PubMed1990

How I help the patient through urodynamic studies.

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Humans↗

PubMed1979

Crohn's disease in children and adolescents: is inadequate weight gain a valid indication for surgery?

Seventy children and adolescents hospitalized for Crohn's disease at the University of Michigan Medical Center between 1966 and 1976 are reviewed. Thirty-three of these children were managed medically and 37 underwent a total of 60 operative procedures. There were 33 bowel resections, 7 appendectomies, 4 abscess drainages, 3 bowel bypasses, and 13 miscellaneous operative procedures. The total operative mortality was 1.7%, and there were 10 complications, all of which were successfully managed. Among the 26 children undergoing bowel resections, 22 were below the third percentile for weight preoperatively. Nearly two-thirds of these gained weight to the 35th percentile following resection. The remainder of the children had a variety of growth and symptomatic responses to surgery. Resection aimed at complete removal of diseased bowel can be expected to yield substantial weight gain in children with Crohn's disease.

Adolescent↗

PubMed1978

ATPase activities in retinal pigment epithelium and choroid.

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Adenosine Triphosphatases↗

PubMed1977

Importance of bicarbonate in retinal function.

This study demonstrates a requirement for bicarbonate in retinal function. Omission of bicarbonate, with either phosphate or Tris used to maintain a constant pH, leads to significant changes in both the electroretinogram potentials and metabolism of the isolated rat retina. Electroretinograms in bicarbonate-free media show a selective loss of the b wave and a decline in the amplitudes of the a wave and Slow PIII. Substitution of phosphate for bicarbonate causes a 60 and 52% decrease in aerobic and anaerobic lactate production, respectively, but this substitution leads to a 27% increase in aerobic retinal ATP content. It is suggested that the electrical effects of bicarbonate-free media are due to a decrease in utilization of ATP below critical levels at critical sites.

Adenosine Triphosphate↗