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Biomedical subjects

M Ptashne

Publications and source records attributed to M Ptashne.

At least 145 records · Page 8Linked to original sources
PubMed1975

Recognition sequences of repressor and polymerase in the operators of bacteriophage lambda.

Nucleotide sequences in two wild-type and six mutant operators in the DNA of phage lambda are compared. Strikingly similar 17 base pair units are found which we identify as the repressor binding sites. Each operator contains multiple repressor binding sites separated by A-T rich spacers. Elements of 2 fold rotational symmetry are present in each of the sites. Superimposed on each operator is an E. coli RNA polymerase recognition site (promoter). Similarities in the sequences of the two lambda promoters, a lac promoter, and an E. coli RNA polymerase recognition site in SV40 DNA are noted.

Base Sequence↗
PubMed1975

Lambda repressor turns off transcription of its own gene.

We report transcription in vitro of the lambda repressor gene, cI, using specific restriction endonuclease fragments as templates. This transcription is repressed by lambda repressor. Moreover, we report the sequence change caused by a cI promoter mutation. This change is located between two repressor binding sites in the rightward operator (OR). Transcription studies using mutant templates indicate that repressor bound to two sites in OR regulates transcription of gene tof, and repressor bound to the remaining site(s) controls transcription of cI.

Base Sequence↗
PubMed1973

Multiple repressor binding at the operators in bacteriophage lambda.

Short DNA duplexes are protected when lambda DNA is digested with nuclease in the presence of lambda repressor. As the ratio of repressor to operator is increased, six successively larger fragments are recovered, ranging in size from 35 to 100 base pairs, each of which binds repressor. Study of these fragments indicates that, at each of the two lambda operators (o(L) and o(R)), repressor first binds to a unique site (not necessarily terminal), and that five additional sites are then filled in linear right-ward or left-ward order. The nucleotide sequences and affinities for repressor of o(L) and o(R) are not identical, although six fragments of similar size are protected at each operator. Evidence is presented arguing against the existence of hairpin-like structures in the operator fragments, and, moreover, it is shown that the operator duplex does not unwind when repressor binds to it.

Autoradiography↗
PubMedDate not supplied

DNA-binding proteins.

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Binding Sites↗
PubMedDate not supplied

Expression of a VHC kappa chimaeric protein in mouse myeloma cells.

The heavy (H) and light (L) chains of antibodies consist of variable (V) and constant (C) regions. The V regions of the heavy and light chains form the antibody combining site. To determine whether a V region could be functional when joined to a polypeptide other than its own C region, we constructed a chimaeric gene encoding the V region of a mouse heavy chain and the C region of a mouse kappa light chain ( VHC kappa). The heavy-chain gene is derived from an A/J mouse hybridoma cell line 36-65 whose antibody product (gamma 1, kappa) is specific for the hapten azophenylarsonate. We report here that, when introduced into a mouse myeloma cell line, the chimaeric gene is expressed and a protein of the expected molecular weight is secreted into the medium. As light chains tend to dimerize we expected that the VHC kappa protein might associate with light chain from the cell line 36-65 to form an antibody-binding molecule. Affinity binding experiments and Ka determination indicate that this is the case. Dimers of this type offer a novel and interesting alternative to existing antibody-binding molecules.

Animals↗