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Biomedical subjects

R B Kent

Publications and source records attributed to R B Kent.

44 records · Page 3Linked to original sources
PubMed1982

Pyrophosphate inhibition of rho ATPase: a mechanism of coupling to RNA polymerase activity.

The effects of pyrophosphate on RNA binding and ATPase activities of Escherichia coli transcription termination factor rho have been studied. Mutant rho-115 protein has a temperature-sensitive RNA-dependent ATPase activity due to the thermolability of binding to RNA [Kent, R.B. & Guterman, S.K. (1981) Fed. Proc. Fed. Am. Soc. Exp. Biol. 40, 1765 (abstr.)]. The presence of either ATP or pyrophosphate at comparable concentrations stabilizes the binary complex of rho and poly(C) at high temperature. ADP at 8-fold greater concentration also stabilizes the mutant rho-RNA binary complex. Pyrophosphate is a noncompetitive inhibitor (Ki = 0.07 mM) of rho poly(C)-dependent ATPase, an activity that is required for rho-mediated termination. These results suggest the existence of a regulatory site on the rho molecule. We suggest that rho NTPase is regulated by RNA polymerase (EC 2.7.7.6) so that during transcription elongation the RNA polymerase competes successfully with rho for substrates and inhibits rho NTPase with product pyrophosphate. Further, RNA polymerase pausing may result in reduced pyrophosphate and increased NTP concentrations, allowing rho NTPase to function.

Adenosine Triphosphatases↗
PubMed1981

A mutant rho ATPase from Escherichia coli that is temperature-sensitive in the presence of RNA.

The Escherichia coli mutant rho-115 suppresses lac operon polarity conferred by the lacZ::IS1 insertion MS319. The ATPase activity of purified rho-115 protein was maximal at 40 degrees C, in contrast to 45 degrees C for rho+. At higher temperatures (50 degrees C, 55 degrees C), the fractions of activities at maximal temperature were consistently lower for rho-115 compared to rho+. The 30-minute time course of rho-115 ATP hydrolysis was linear at 37 degrees C but at 45 degrees C the linear kinetics of hydrolysis reached a plateau between 10 and 15 minutes. The 30-minute time courses for rho+ were linear at both 37 degrees C and 45 degrees C. The rho-115 and rho+ ATPase activities were equally heat-stable during preincubation at 45 degrees C in buffer. Inclusion of ATP during preincubation protected these rho proteins from inactivation to the same extent. The presence of polyC during preincubation protected rho+ activity but produced substantial inactivation of rho-115 ATPase. The presence of polyU during preincubation gave similar results. Concentrations of polyC between 625 ng/ml and 100 micrograms/ml yielded the same extent of rho-115 ATPase inactivation during preincubation at 45 degrees C. Thermal inactivation of rho-115 ATPase by polyC was halted by shifting preincubation temperature from 45 degrees C to 35 degrees C, indicating that polyC-induced destabilization of rho-115 was irreversible.

Adenosine Triphosphatases↗
PubMed1981

Nonfunctioning islet cell tumors.

In nonfunctioning islet cell tumors of the pancreas, hormone production is not clinically evident. This type of tumor constituted 15% of all islet cell tumors seen at the Mayo Clinic from 1960 through 1978. Although identical to functioning islet cell tumors embryologically and histologically, the nonfunctioning tumors differ in presentation, location, size, and rate of malignancy. At admission to the hospital, patients often have pain or jaundice due to a large, solid, solitary lesion that occurs most commonly in the head of the pancreas. Extended survival is not excluded by the high malignancy rate (92%) of these slow-growing tumors. The survival rates at three and five years were 60% and 44%, respectively, even though most patients had metastatic disease at the time of exploration.

Adenoma, Islet Cell↗
PubMed1980

Cell-cycle properties and proliferation kinetics of late erythroid progenitors in murine bone marrow.

The cell-cycle properties of marrow CFUE were assessed in normal regenerating cell preparations. In addition, the erythropoietin sensitivity of CFUE was correlated to the cell-cycle distribution of these cells. The results suggest a coupling of erythropoietin sensitivity to the S-phase of the CFUE cell cycle in so far as CFUE in G2/M/G1 were 2 to 10 times less sensitive to the hormone. It is concluded that the CFUE cell cycle per se is not a focus for erythropoietic regulation.

Animals↗
PubMedDate not supplied

Thoracoscopic ligation of the thoracic duct.

Traditional operative management for chylous drainage refractory to conservative therapy is thoracic duct ligation via right open thoracotomy. This case report details successful thoracoscopic ligation of the thoracic duct for a chylous leak following a left neck dissection. Since the thoracoscopic approach is less morbid than open thoracotomy, early operative management is recommended for thoracic duct injuries.

Adult↗
PubMedDate not supplied

Transcriptional activation of immunoglobulin alpha heavy-chain genes by translocation of the c-myc oncogene.

Our previous studies with the mouse myeloma MOPC 315 (IgA, lambda 2) cell line, using myeloma mutants that had deleted the productive alpha heavy (H)-chain gene, had shown that the excluded alpha constant-region (C alpha) allele in these cells is transcriptionally active. Recent reports from several laboratories have demonstrated that in many BALB/c mouse myelomas, including MOPC 315, the DNA segment encoding the c-myc oncogene is translocated to a C alpha allele. The mRNA coding strand of DNA for the c-myc gene is on the opposite strand from the immunoglobulin gene in this locus. We have now investigated the relationship between the c-myc translocation and transcriptional activity of excluded C alpha alleles in IgA- and IgG-producing mouse myeloma lines. We report here that c-myc-C alpha recombination events correlate with demethylation and transcription of C alpha genes. Several novel C alpha RNA species are produced, which are transcribed from the immunoglobulin-gene sense strand. The larger C alpha RNAs appear to contain c-myc sequences. Thus the anti-sense strand of the c-myc gene provides a promoter for transcription of the C alpha gene. This result suggests that in other transformed cells with a c-myc-immunoglobulin gene translocation, including many Burkitt's lymphomas, activation of the adjacent immunoglobulin gene would occur.

Animals↗