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G Klock

Publications and source records attributed to G Klock.

23 records · Page 2Linked to original sources
PubMed1984

Nucleotide sequence of the repressor gene of the RA1 tetracycline resistance determinant: structural and functional comparison with three related Tet repressor genes.

The tetracycline resistance determinant of RA1 was cloned. It consists of at least two genes oriented with opposite polarity, tetA for resistance and tetR for regulation. The transcriptional control sequence was identified and analyzed. It consists of overlapping promotors with divergent orientation and a tandem arrangement of operators. Nucleotide sequencing revealed two open reading frames. One codes for a protein which was identified as a Tet repressor by comparing its primary structure with those of other Tet repressors. The RA1 tetR gene codes for 218 amino acids with a calculated molecular weight of 24.4 kDa. In the primary sequence of the RA1-, pSC101-, Tn10-, and RP1/Tn1721-encoded Tet repressors, 36% of the amino acids are identical. This homology is clustered within the first 150 amino acids, 49% of which are identical among all four proteins. These results are discussed with respect to their structure and function in comparison to other DNA binding proteins.

Amino Acid Sequence↗
PubMed1984

Construction of an E. coli strain overproducing the Tn10-encoded TET repressor and its use for large scale purification.

Overproduction of the repressor protein from the Tn10-encoded tetracycline resistance operon is achieved by placement of the respective gene under control of bacteriophage lambda promoter PL in a vector-host system. All cloning steps have to be carried out under repressed conditions to assure survival of the cell. The cI 857 mutation is used to control expression of the tetR gene in large scale fermentation. After induction, the overproducing Escherichia coli strain continues to grow for 2.5 generations before growth terminates. In the expression phase, active TET repressor comprises up to 13% of the total soluble protein. A procedure is described to purify the TET repressor protein to homogeneity on a large scale. Starting from a 10 litre culture, approximately 250 mg of homogeneous, active TET repressor are obtained. The amino acid sequence of the N and C termini are in agreement with the gene start and stop determined from the nucleotide sequence of the Tn10 tetR gene.

Cloning, Molecular↗
PubMed1982

Analysis of tet operator-TET repressor complexes by thermal denaturation studies.

Interaction of the Tn10 encoded TET repressor with the tet operator is studied by thermal denaturation of the specific complexes employing operator containing purified DNA restriction fragments varying in length from 187 bp to 501 bp. Comparison of the melting curves obtained with the free DNA and DNA.repressor complexes revealed a specific stabilisation of the operator containing cooperatively melting segment in multiphasic denaturation curves. Under limiting concentrations of TET repressor the denaturation of the free DNA is observed next to the denaturation of the repressor.DNA complex. Quantitative analysis yields a binding curve with a stoichiometry of four TET repressors per tet operator containing fragment. The denaturation temperature of the complex is almost independent of the ionic strength indicating that the protein component denatures at this temperature. The half life time of the TET repressor.tet operator complex is greater than 100 min under these conditions. The tet operator on the 187 bp fragment is determined to be located between a Xba I and a Sau 3a site by removing base pairs from either end of the fragment and subsequent comparison of the melting curves. It is concluded that the TET repressor recognizes the double stranded rather than a possible cruciform structure of the tet operator. The influence of a regulatory protein on the thermal stability of a genetic control region is discussed with respect to its possible influence on the initiation of transcription.

Base Composition↗
PubMedDate not supplied

Oestrogen and glucocorticoid responsive elements are closely related but distinct.

DNA sequences recognized by the glucocorticoid receptor are termed glucocorticoid-responsive elements because of their stimulatory effect on transcription. An oligonucleotide of 15 base pairs having partial or perfect symmetry is necessary for glucocorticoid induction and this same oligonucleotide is surprisingly also recognized by the progesterone receptor. Here we define a palindromic sequence of 15 base pairs, modelled after a sequence element shared by the vitellogenin genes of frog and chicken, which confers oestrogen inducibility on a heterologous promoter and can be converted into a glucocorticoid-responsive element by substitution of one or two bases at homologous positions in the palindrome. Considered with the observation that the DNA-binding domains of steroid receptors are closely related, this finding demonstrates that the steroid-responsive elements constitute a family of related DNA sequences.

Base Sequence↗