Biomedical subjects

P Traub

Publications and source records attributed to P Traub.

At least 163 records · Page 9Linked to original sources

PubMed1977

Fate of histone messenger RNA in mengovirus-infected Ehrlich ascites tumor cells.

Histone mRNA was isolated from mengovirus-infected Ehrlich ascites tumor cells at various times postinfection and quantitated in a reticulocyte cell-free protein-synthesizing system. The amount of translatable histone mRNA decreases during the first hour postinfection by 30%, rises during the following 1-1.5 h by 10-15%, drops progressively in the further course of infection, and reaches 20% of the control at the end of the infectious cycle (8-9 h postinfection). On the basis of the relative histone mRNA contents, the histone-synthesizing potentials of mengovirus-infected Ehrlich ascites tumor cells are substantially higher throughout infection than actually expressed in vivo. This result indicates that the virus-induced shutoff of histone synthesis is not directly the consequence of inactivation or degradation of histone mRNA. Most of the histone mRNA recovered from mengovirus-infected Ehrlich ascites tumor cells is bound to ribosomes. Late in infection, certain mRNAs are co-isolated with histone mRNAs, very likely due to loss or shortening of poly(A) occurring after release of the mRNAs from polyribosomes.

Animals↗

PubMed1977

An investigation of the stability of messenger RNAs in cell-free, translational systems from uninfected and mengovirus-infected Ehrlich ascites tumor cells.

The stabilities and translation of Ehrlich ascites tumor cell poly(A)-containing mRNA and mengovirus RNA in fractionated cell-free protein synthesizing systems from uninfected and mengovirus-infected Ehrlich ascites tumor cells were studied. During incubation of the systems about 20% of the input RNA is reduced in size and associated with ribosomes engaged in polypeptide synthesis; the remainder is rapidly degraded by RNases. At the end of active translation, both mRNA and nascent proteins are bound to polysomes which are of the same size as those formed during active protein synthesis. The kinetics of protein synthesis closely follow those of RNA hydrolysis. The stabilities of mengovirus RNA and poly(A)-containing mRNA from Ehrlich ascites tumor cells are the same in both systems.

Animals↗

PubMed1977

2'(3'),5'-ADP inhibits initiation-dependent protein synthesis in a cell-free system from Ehrlich ascites tumor cells.

When tested in a poly(U)-dependent polyphenylalanine synthesizing system and in a postnuclear supernatant, both derived from Ehrlich ascites tumor cells, 2'(3'),5'-ADP did not affect chain elongation of polypeptide synthesis. In a cell-free system which was dependent on initiation and programmed by natural mRNA, however, the amino acid incorporating activity was suppressed to about 10% of the control in the presence of 1 mM 2'(3'),5'-ADP. The inhibitor was shown not to interfere with the attachment of poly(U) to the small ribosomal subunit and with the formation of mRNA-80S ribosome complexes in a complete protein synthesizing system. The subsequent attachment of a 40S ribosomal subunit to the mRNA-80S ribosome complex and the formation of polysomes, however, was depressed by the inhibitor. The experimental results suggest that 2',(3'),5'-ADP inhibits initiation-dependent protein synthesis between monosome formation and the formation of the first peptide bond(s).

Adenosine Diphosphate↗

PubMed1977

Coding capacity of poly(A)+mRNA isolated from mengovirus-infected Ehrlich ascites tumor cells.

Total poly (A)+mRNA was isolated from mengovirus-infected Ehrlich ascites tumor cells at various times postinfection and quantitated in a cell-free system derived from uninfected ascites cells. Basic proteins were separated from acidic proteins by carboxymethyl cellulose chromatography. At the end of the infectious cycle, 8h postinfection, the cellular contents of most mRNAs coding for basic ribosomal proteins are still between 70 and 90 percent of those measured at the beginning of infection or in uninfected cells. On the basis of this result, the rapid shutoff of host protein synthesis after mengovirus infection of Ehrlich ascites tumor cells cannot be the consequence of the inactivation of host template RNA.

Animals↗

PubMed1977

Alteration of the intracellular energetic and ionic conditions by mengovirus infection of Ehrlich ascites tumor cells and its influence on protein synthesis in the midphase of infection.

Mengovirus infection of Ehrlich ascites tumor cells caused a change of the intracellular ATP concentration. It increased by 35% within the first 3 h postinfection and then declined to zero within the next 5 h. The decrease in the ATP concentration was due, at least in part, to leakage of ATP into the medium, where it could be demonstrated by the luciferin-luciferase assay. Gross leakage of ATP was observed at 4.5 h postinfection, concomitant with the production of the first intracellular, infectious virus particles. A similar concentration decrease was detected for Mg(2+), the polyamines, and K(+), whereas an increase in the Na(+) concentration was observed. The intracellular Mg(2+) concentration varied synchronously with the ATP level, rising by 16% during the first 3 h postinfection and then progressively falling to lower values in the late period of the infectious cycle. After an initial slight enhancement, the putrescine, spermidine, and spermine concentrations declined at about 1.5 h postinfection. Wherease the intracellular K(+) concentration increased by 17% during the first hour postinfection, the Na(+) concentration diminished by the same value within the same time period, leaving the internal ionic strength unchanged early in infection. Three hours after the beginning of virus infection, there was a rapid decline of K(+) and enhancement of Na(+) within the cell. These alterations of the intracellular energetic and ionic conditions seem to be, at least in part, responsible for the cessation of virus-specific protein synthesis in mengovirus-infected Ehrlich ascites tumor cells commencing 3 to 3.5 h postinfection.

Adenosine Triphosphate↗

PubMed1977

Shutoff of histone synthesis by Mengovirus infection of Ehrlich ascites tumor cells.

The histone synthesizing capacity of mengovirus-infected Ehrlich ascites tumor cells and of their corresponding postnuclear supernatants was investigated as a funcion of time post-infection. In addition, histone synthesis was compared with the synthesis of other basic host proteins under identical conditions. In the scope of mengovirus infection of Ehrlich ascites tumor cells the less complex fraction comprising basic protein, separated from the acidic proteins by carboxymethyl cellulose chromatography, can be regarded as a representative of total host protein. Histones and the remaining basic host proteins therefore are well suited as easily identifiable indicators of the host protein synthesizing potential of mengovirus-infected Ehrlich ascites tumor cells. The cessation of histone synthesis proceeds faster than the arrest of the synthesis of other basic host protein.

Animals↗

PubMed1977

Inhibition of ribonucleases by ribonucleotides and transition state analogs in cell-free extracts from Ehrlich ascites tumor cells.

We investigated the ribonucleolytic breakdown of poly(U), poly(A), RNA trascribed from calf thymus DNA with E. coli RNA polymerase, ribosomal RNA, tRNA and mengovirus RNA by an enzyme fraction obrained from a postribosomal supernatant of Ehrlich ascites tumor cells. The single-stranded homopolyribonucleotides are preferentially degraded by the enzyme fraction with the production of ribonucleoside 5'-monophosphates. The RNase activity is completely dependent on the presence of Mg2+ ions and is highest at Mg2+ and K+ concentrations optimal for cell-free protein synthesis. Ribonucleoside 5'-monophosphates, ribonucleoside 2'(3')-monophosphates, ribonucleoside 2'(3'),5'-bisphosphates and transition state analogs consisting of vanadyl sulfate and either ribonucleosides or ribonucleoside 5'-monophosphates in a molar ratio 1:1 inhibit the ribonucleolytic activity of the enzyme fraction. The ribonucleoside 2'(3'),5'-bisphosphates and the transition state analogs are the most effective inhibitors. However, only in the presence of ribonucleoside 2'(3'),5'-bisphosphates a concomitant stimulation by 50 to 60% of poly(U)-directed polyphenylalanine synthesis is observed; all the other RNase inhibitors tested also inhibit polypeptide synthesis. The results of preliminary experiments show that poly(U) and ribonucleoside 2'(3'),5'-bisphosphates are well suited as ligands for affinity chromatography of ribonucleases from Ehrlich ascites tumor cells.

Animals↗

PubMed1976

Protein synthesis in postnuclear supernatants from mengovirus-infected Ehrlich ascites tumor cells.

The effect of mengovirus infection on the protein synthetic capacity of Ehrlich ascites tumor cells cultured in vitro was studied in vivo and in vitro employing postnuclear supernatants prepared at various times post-infection in the absence and in the presence of 1% Triton X-100. The amino acid incorporating activities of extracts obtained in the presence of the detergent were reduced by about 30% compared with the capacities of the corresponding postnuclear supernatants prepared in the absence of Triton X-100; but the course of the activity vs. time curve was not influenced by the detergent. Under the conditions employed, the postnuclear supernatants were unable to reinitiate protein synthesis once elongation of nascent polypeptide chains concomitant with ribosome runoff was completed. After mengovirus infection, a gradual disappearance of polysomes from postnuclear supernatants and a simultaneous accumulation of monosomes was observed. The protein-synthesizing activities of normal and infected cells were inversely proportional to the monosome concentrations of their corresponding extracts. Qualitatively, protein synthesis in intact cells and in postnuclear supernatants responded similarly to mengovirus infection. In both cases an initial reduction of host-specific amino acid incorporation was followed by a burst of viral protein synthesis. However, the two activity vs. time curves showed the following significant differences: 1) The activities of extracts from control cells and from mengovirus-infected cells nearly in the infectious cycle were low compared with the activities observed in vivo. 2) In the middle of the infectious cycle, the peak of viral protein synthesis occurred later and the activity was higher in vitro. 3) Finally, in the late period of the infectious cycle the postnuclear supernatants had considerable protein synthesizing activity, at a time when protein synthesis in vivo was nil.

Animals↗

PubMed1972