Biomedical subjects
Publications and source records attributed to P Keim.
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Bovine liver rhodanese is a single polypeptide of 293 amino acids in which the halves of the molecule assume analogous tertiary structures in the absence of substantial sequence homology. The sulphur atom transferred during catalysis is bound in persulphide linkage to Cys-247. Substrate binding seems to involve Arg-186 and Lys-249.
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The covalent structure of apolipoprotein A-II, isolated from the serum high-density lipoprotein of a single male Rhesus monkey (Macaca mulatta), was determined. The amino acid sequence of this 77-residue polypeptide is: less than Glu-Ala-Glu-Glu-Pro5-Ser-Val-Glu-Ser-Leu10-Val-Ser-Gln-Tyr-Phe15-Gln-Thr-Val-Thr-Asp20-Tyr-Gly-Lys-Asp-Leu25-Met-Glu-Lys-Val-Lys30-Ser-Pro-Glu-Leu-Gln35-Ala-Gln-Ala-Lys-Ala40-Tyr-Phe-Glu-Lys-Ser45-Lys-Glu-Gln-Leu-Thr50-Pro-Leu-Val-Lys-Lys55-Ala-Gly-Thr-Asp-Leu60-Val-Asn-Phe-Leu-Ser65-Tyr-Phe-Val-Glu-Leu70-Arg-Thr-Gln-Pro-Ala75-Thr-Gln-COOH. A comparison of this structure to that of the monomeric form of human apolipoprotein A-II reveals a high degree of homology except for six conservative amino acid replacements (positions 3, 6, 40, 53, 59, and 71). Of particular structural significance is the replacement of cysteine by serine in position 6. This explaines why Rhesus A-II exists in monomeric form, contrary to the established dimeric nature of the human protein.
Whole nucleic acid fractions of isolated rat islets of Langerhans greatly stimulate incorporation of radioactive amino acids into protein in a wheat germ ribosomal system. Approximately 30% of the synthetic product is precipitated with antisera to insulin or proinsulin. Characterization of this material by gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a molecular mass of 11,500 daltons. Trypsin digestion releases intact A chain as well as tryptic fragments of the C-peptides and B chains of the two rat proinsulins. Automated sequence determination of labeled cell-free product purified by immunoprecipitation discloses the presence of 23 additional amino acids NH2-terminal to the B chain sequence of proinsulin. The partial amino acid sequence of this extension is as follows: NH2-X-Leu (Lys) Met-x-Phe-Leu-Phe-Leu-Leu (Lys) Leu-Leu-x-leu-X-X-X-X-X-X-X-X-proinsulin. On the basis of the above evidence we have designated this peptide preproinsulin.
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Formation of (13)C-resonances attributable to carbamino derivatives has been observed in human erythrocyte hemolysate preparations equilibrated with (13)CO(2) at 33 degrees . Carbamino formation is most marked in deoxyhemoglobin and at alkaline pH, and is very largely inhibited by the addition of 2,3-diphosphoglycerate or conversion to oxyhemoglobin. The prominent carbamino resonance at 30.0 ppm upfield of CS(2) is visible in the spectrum of packed, deoxygenated erythrocytes equilibrated in (13)CO(2). This chemical shift falls close to that observed with sperm-whale myoglobin and within 2 ppm upfield of that seen with simple amino acids and peptides. The bicarbonate-carbonate resonance near 33 ppm is broad in the hemoglobin preparations, which always contain some carbonic anhydrase, but becomes narrow in the presence of the carbonic anhydrase inhibitor, acetazolamide. The nuclear magnetic resonance condition of intermediate exchange rate with dissolved CO(2) (68.4 ppm) obtains in the absence of inhibitor. The process has marked consequences in reducing the spin-lattice relaxation time, T(1), of the bicarbonate resonance by more than 10 times. The deoxyhemoglobin carbamino resonance has a T(1) value of 700 msec, indistinguishable from that of the protein carbonyl resonance envelope.
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Escherichia coli generalized recombination, utilizing the RecA RecB recombination pathway, requires large stretches (70-200 bp) of complete DNA sequence homology. In contrast, we have found that the RecE pathway can promote recombination between DNA with only short stretches of homology. A plasmid containing 10 partially homologous direct repeats was linearized by digestion with specific restriction enzymes. After transformation, a RecE+ (sbcA) host was able to circularize the plasmid by recombination between partially homologous direct repeat sequences. Recombination occurred in regions of as little as 6 bp of perfect homology. Recombination was enhanced in the regions adjacent to restriction sites used to linearize the plasmid, consistent with a role of double-strand breaks in promoting recombination. A mechanism is proposed in which the 5' exonuclease, ExoVIII, produces 3' single-stranded ends from the linearized plasmid. These pair with other sequences of partial homology. Partial homologies in the sequences flanking the actual join serve to stabilize this recombination intermediate. Recombination is completed by a process of "copy and join." This recombination mechanism requires less homology to stabilize intermediates than the degree of homology needed for mechanisms involving strand invasion. Its role in nature may be to increase genomic diversity, for example, by enhancing recombination between bacteriophages and regions of the bacterial chromosome.
A 356-marker linkage map of Glycine max (L.) Merr. (2n = 20) was established by anchoring 106 RAPD markers to an existing RFLP map built with a large recombinant inbred line population (330 RILs). This map comprises 24 major and 11 minor linkage groups for this genome which is estimated to be approximately 3,275 cM. The RAPD markers show similar distribution throughout the genome and identified similar levels of polymorphism as the RFLP markers used in the framework. By using a subset population to anchor the RAPD markers, it was possible to enhance the throughput of selecting and adding reliable marker loci to the existing map. The procedures to generate a dependable genetic linkage map are also described in this report.