Control elements of the tetracycline-resistance operon encoded in Tn10 of Escherichia coli have been utilized to establish a highly efficient regulatory system in mammalian cells. By fusing the tet repressor with the activating domain of virion protein 16 of herpes simplex virus, a tetracycline-controlled transactivator (tTA) was generated that is constitutively expressed in HeLa cells. This transactivator stimulates transcription from a minimal promoter sequence derived from the human cytomegalovirus promoter IE combined with tet operator sequences. Upon integration of a luciferase gene controlled by a tTA-dependent promoter into a tTA-producing HeLa cell line, high levels of luciferase expression were monitored. These activities are sensitive to tetracycline. Depending on the concentration of the antibiotic in the culture medium (0-1 microgram/ml), the luciferase activity can be regulated over up to five orders of magnitude. Thus, the system not only allows differential control of the activity of an individual gene in mammalian cells but also is suitable for creation of "on/off" situations for such genes in a reversible way.

https://www.pnas.org/content/pnas/89/12/5547.full.pdf

Tight control of gene expression in mammalian cells by tetracycline-responsive promoters.

Pathology and genetics of tumors of soft tissue and bone

The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53

The cell cycle is composed of a series of steps which can be negatively or positively regulated by various factors. Chief among the negative regulators is the p53 protein. Alteration or inactivation of p53 by mutation, or by its interactions with oncogene products of DNA tumour viruses, can lead to cancer. These mutations seem to be the most common genetic change in human cancers.

The p53 tumour suppressor gene

Deletions or mutations of the retinoblastoma gene, RB1, are common features of many tumors and tumor cell lines. Recently, the RB1 gene product, p105-RB, has been shown to form stable protein/protein complexes with the oncoproteins of two DNA tumor viruses, the adenovirus E1A proteins and the simian virus 40 (SV40) large T antigen. Neither of these viruses is thought to be associated with human cancer, but they can cause tumors in rodents. Binding between the RB anti-oncoprotein and the adenovirus or SV40 oncoprotein can be recapitulated in vitro with coimmunoprecipitation mixing assays. These assays have been used to demonstrate that the E7 oncoprotein of the human papilloma virus type-16 can form similar complexes with p105-RB. Human papilloma virus-16 is found associated with approximately 50 percent of cervical carcinomas. These results suggest that these three DNA viruses may utilize similar mechanisms in transformation and implicate RB binding as a possible step in human papilloma virus-associated carcinogenesis.

https://science.sciencemag.org/content/sci/243/4893/934.full.pdf

The human papilloma virus-16 E7 oncoprotein is able to bind to the retinoblastoma gene product

https://www.cell.com/cell/pdf/0092-8674(88)90559-4.pdf

SV40 large tumor antigen forms a specific complex with the product of the retinoblastoma susceptibility gene

We compare two commonly used diagnostic approaches, one relying on plasma bicarbonate concentration and “anion gap,” the other on “base excess,” with a third method based on physicochemical principles, for their value in detecting complex metabolic acid‐base disturbances. We analyzed arterial blood samples from 152 patients and nine normal subjects for pH, P CO 2 , and concentrations of plasma electrolytes and proteins. Ninety-six percent of the patients had serum albumin concentration < 3 SD below the mean of the control subjects. In about one-sixth of the patients, base excess and plasma bicarbonate were normal. In a great majority of these apparently normal samples, the third method detected simultaneous presence of acidifying and alkalinizing disturbances, many of them grave. The almost ubiquitous hypoalbuminemia confounded the interpretation of acid‐base data when the customary approaches were applied. Base excess missed serious acid‐base abnormalities in about one-sixth of the patients; this method fails when the plasma concentrations of the nonbicarbonate buffers (mainly albumin) are abnormal. Anion gap detected a hidden “gap acidosis” in only 31% of those samples with normal plasma bicarbonate in which such acidosis was diagnosed by the third method; when adjusted for hypoalbuminemia, it reliably detected the hidden abnormal anions. The proposed third method identifies and quantifies individual components of complex acid‐base abnormalities and provides insights in their pathogenesis.

https://www.atsjournals.org/doi/pdf/10.1164/ajrccm.162.6.9904099

Diagnosis of Metabolic Acid–Base Disturbances in Critically Ill Patients

ObjectivesTo show how hypoalbuminemia lowers the anion gap, which can mask a significant gap acidosis; and to derive a correction factor for it.DesignObservational study.SettingIntensive care unit in a university-affiliated hospital.SubjectsNine normal subjects and 152 critically ill patients (265 m

Anion gap and hypoalbuminemia.

KRUPPEL (Kr), one of the zygotically active Drosophila segmentation genes, is expressed in a restricted domain during the blastoderm stage of embryogenesis and is involved in the control of development of the thoracic and abdominal segments of the fly1. Kr encodes a polypeptide containing DNA-binding zinc-finger motifs2, disruptions of which yield Kr mutants3,4. We have assayed the transcriptional activities of wild-type Kr protein as well as Lac repressor/Kr fusion proteins in HeLa and CV-1 cells. Wild-type Kr and a Lac–Kr chimaeric protein repressed transcription from reporter promoters in which a consensus Kr binding site derived from sequences within the even-skipped promoter5 had been inserted in an upstream position. We mapped the repression function of Kr to an alanine-rich amino-terminal region of the protein, as a Lac/Kr fusion protein containing only amino acids 26–110 of Kr repressed transcription from a reporter promoter containing upstream lac operators. This demonstrates that the DNA-binding and repression activities of the Kr protein are distinct. These data are consistent with genetic evidence that Kr represses even-skipped6,7 and hunchback8 expression, and suggest that Kr is a negative regulator of transcription in Drosophila.

Drosophila Krüppel protein is a transcriptional represser

https://www.cell.com/cell/pdf/0092-8674(88)90409-6.pdf

James Figge

Papers

SV40 large tumor antigen forms a specific complex with the product of the retinoblastoma susceptibility gene

Diagnosis of Metabolic Acid–Base Disturbances in Critically Ill Patients

Anion gap and hypoalbuminemia.

Drosophila Krüppel protein is a transcriptional represser

Stringent regulation of stably integrated chloramphenicol acetyl transferase genes by E. coli lac repressor in monkey cells