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Biomedical subjects

I Zabin

Publications and source records attributed to I Zabin.

At least 55 records · Page 3Linked to original sources
PubMed1974

Beta-galactosidase from termination and deletion mutant strains.

beta-Galactosidase fragments were isolated from strains of Escherichia coli with mutations in the lacZ gene. The polypeptide obtained from a termination mutant (lacZNG125) appeared to be the intact gene product, containing the first half of the beta-galactosidase amino acid sequence. From an internal deletion mutant strain (lacZU163), an aggregate was obtained of several partially degraded polypeptides. Each of these was smaller than predicted from genetic data for the fragment. Introduction of the lacZU163 mutation into a protein degradation-deficient strain (Deg(-)) resulted in the protection of the amino-terminal region of the protein. Some of the BrCN peptides from the U163 polypeptides were separated and identified. From such experiments it was shown that in both Deg(-) and Deg(+) strains the COOH-terminal region is rapidly degraded. This indicates that the complete gene product of lacZU163 has not been detected. The use of genetically defined enzyme fragments in studying structure-function relationships and in determination of primary structure is discussed.

Amino Acid Sequence↗
PubMed1972

-Galactosidase: immunological activity of ribosome-bound, growing polypeptide chains.

Ribosomes carrying nascent chains of beta-galactosidase were prepared by disruption of Escherichia coli in detergent-free buffer of high salt concentration, followed by purification on a discontinuous sucrose gradient. Assay by the method of immune hemolysis inhibition with anti-beta-galactosidase indicated that considerable amounts of antibody were bound by the growing chains. Much of the crossreacting material could be released from the ribosomes by treatment with puromycin. The ability to bind anti-beta-galactosidase was completely destroyed when ribosomes were heated at 60 degrees C. At very early times after induction, well before the appearance of active enzyme, crossreacting material could be demonstrated on ribosomes; this finding correlated with the appearance of an amino-terminal fragment of beta-galactosidase. Thus, growing chains of beta-galactosidase must begin to fold before their release from the ribosome.

Animals↗
PubMed1970

Beta-galactosidase: isolation of and antibodies to incomplete chains.

A prematurely terminated polypeptide chain was purified to homogeneity from an Escherichia coli amber mutant strain containing the site of the mutation in the beta-galactosidase structural gene. The polypeptide was highly active against anti-beta-galactosidase, and had an amino acid composition similar to but not identical to that of beta-galactosidase. The molecular weight of the reduced, carboxymethylated chain in 6 m guanidine hydrochloride was found to be 89,000, in excellent agreement with the size predicted from the position of the mutation. This result adds further support to the conclusion that the gene specifies the structure of a single polypeptide chain. Antisera were prepared against partially purified preparations of this polypeptide and a similar one, of molecular weight about 100,000, produced by another amber mutant. These sera had lower titers towards beta-galactosidase than anti-beta-galactosidase. In the double-diffusion test, they reacted towards extracts of nonsense and deletion mutant strains in a pattern similar to that previously observed with anti-beta-galactosidase. A sensitive immunological test for cross-reacting protein was devised based on the inhibition by beta-galactosidase of the reaction between such protein and antibodies prepared against incomplete chains.

Amino Acids↗
PubMed1966

Co-linearity of beta-galactosidase with its gene by immunological detection of incomplete polypeptide chains.

Many nonsense mutants that map in the beta-galactosidase structural gene produce material that forms precipitin lines when tested by double diffusion on agar against antiserum prepared from native beta-galactosidase. Relative sizes of the cross-reacting materia!s measured by sucrose density gradient centrifugation are the same as sizes calculated from genetic mapping of nonsense mutants. Orientation of the protein to its gene is also indicated.

Chromosome Mapping↗