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Biomedical subjects

D Zipser

Publications and source records attributed to D Zipser.

At least 37 records · Page 2Linked to original sources
PubMed1979

Purification and characterization of protease III from Escherichia coli.

An endoproteolytic enzyme of Escherichia coli, designated protease III, has been purified about 9,600-fold to homogeneity with a 6% yield. The purified enzyme consists of a single polypeptide chain of Mr 110,000 and is most active at pH 7.4. Protease III is very sensitive to metal-chelating agents and reducing agents. The EDTA-inactivated enzyme can be reactivated by Zn2+, Co2+ or Mn2+. Protease III is devoid of activity toward aminopeptidase, carboxypeptidase, or esterase substrates but rapidly degrades small proteins. When fragments of beta-galactosidase are used as substrates for protease III, the enzyme preferentially degrades proteins with molecular weights of less than 7,000. Protease III cleaves the oxidized insulin B chain at two sites with an initial rapid cleavage at Tyr-Leu (16-17) and a second slower cut at Phe-Tyr (25-26).

Cations, Divalent↗
PubMed1979

Isolation and characterization of mutations in the structural gene for protease III (ptr).

Escherichia coli mutants defective in protease III were isolated by enzyme assays of heavily mutagenized colones. One mutant produced thermolabile enzyme, and it is presumed to have a mutation in the structural gene of protease III. Two other mutants mapping at the same site had less than 5% of the wild-type protease III level. The genetic locus of these mutations, designated ptr, was located at approximately 60 min on the E. coli linkage map based on its high frequency (70%) of contransduction by P1 with argA. Strains with less than 5% of the wild-type protease III activity grew normally and degraded nonsense fragments of beta-galactosidase at wild-type rates.

Chromosome Mapping↗
PubMed1978

Deg phenotype of Escherichia coli lon mutants.

Deg. one of the Escherichia coli systems for degrading abnormal polypeptides (e.g., nonsense fragments), is also involved in the degradation of some classes of missense proteins. Both missense proteins of beta-galactosidase and temperature-sensitive phage products appear to be degraded by the Deg system. Mutations in the Deg system are indistinguishable from mutations classically called lon or capR; all map near proC, all are mucoid, defective in protein degradation, sensitive to radiomimetic agents, and defective in P1 lysogenization. All are able to propagate temperature-sensitive phage better than lon+ parental strains. Mutations that suppress the radiation sensitivity of these strains (sul) also suppress the P1 lysogenization defect, but do not affect mucoidy or the degradation defect.

Bacterial Proteins↗
PubMed1977

Mapping of restriction sites in the attachment site region of bacteriophage lambda.

A find structure map of the EcoRI fragment containing the lambda attachment-site region has been constructed. 38 different restriction endonucleases have been employed and 170 sites located in this fragment. In addition, sites in adjacent regions have been determined for several enzymes. Complete cleavage maps of the entire lambda genome have been obtained for endonucleases BglII, BluI, KpnI, SacI, SacII, SalI and XbaI. The strategy employed for mapping included comparison of deletion and substitution mutants, analysis of mixed digests, and detailed analysis of subfragments.

Chromosome Mapping↗
PubMed1977

Degradation of Escherichia coli beta-galactosidase fragments in protease-deficient mutants of Salmonella typhimurium.

The degradation rates of several mutationally generated fragments of Escherichia coli beta-galactosidase were determined in wild-type strains of Salmonella typhimurium and in mutant Salmonella strains lacking several proteases and peptidases. Three termination fragments (produced by lacZ545, lacZ521, and lacZX90) and one internal reinitiation (restart) fragment [lacZpi(1)] are degraded in wild-type Salmonella strains at the same rates observed in wild-type Escherichia coli strains. Mutations that lead to loss of peptidases N, A, B, P, and Q or to loss of protease I or II do not affect the decay rates of any of these fragments. In addition, all of these peptidases and proteases are present in E coli mutants carrying deg mutations (deg mutations are known to stabilize beta-galactosidase fragments). Apparently, none of the proteases and peptidases that are currently accessible to direct genetic analysis plays a role in the early steps of the degradation of protein fragments.

Escherichia coli↗
PubMed1976

Transfection of Escherichia coli by Mu DNA.

Infectivity of Mu DNA was demonstrated in Ca+ +-treated Escherichia coli cells that lacked the nucleases Exo V and Endo I. The efficiency of transfection is about 10(-7) per phage equivalent. Infectivity is destroyed by denaturation of Mu DNA, and cannot be restored by renaturation.

Calcium↗
PubMed1976

Missense mutations in the lacZ gene that result in degradation of beta-galactosidase structural protein.

Thirty-two missenese mutations were found among more than 200 independently induced mutations in the lacZ gene of Escherichia coli. Twenty of these missense mutations were induced by nitrosguandine, and 12 were induced by aminopurine. The lacZ structural protein was endogenously degradable in seven of the mutant strains; the mutations in these strains were found to lie at only three sites in the lacZ gene. Five of the seven independent mutations were at a single site, and some heterogeneity in the degradation of the lacZ protein was observed within these mutant strains.

Chromosome Mapping↗
PubMed1973

In vivo splicing of protein: one continuous polypeptide from two independently functioning operons.

Active-beta-galactosidase (EC 3.2.1.23) is often formed in rec(-) merozygotes containing a pair of mutations in the z gene of the lac operon. Contrary to expectation, with certain pairs of mutants this enzyme, upon dissociation, does not yield two independent polypeptides but only a single continuous protomer. Both genetic recombination and suppression have been ruled out as the source of this phenomenon. Therefore we believe we are observing the synthesis of one protein from two independently functioning genes.

Bacterial Proteins↗