Search PubMed⌕ Search

Biomedical subjects

C E Samuel

Publications and source records attributed to C E Samuel.

At least 127 records · Page 7Linked to original sources
PubMed1980

Mechanism of interferon action: simian virus 40-specific early polypeptides synthesized in untreated and interferon-treated monkey kidney cells.

The effect of interferon treatment on proteins synthesized in simian virus 40 (SV40)-infected cells in the presence of cytosine arabinoside was investigated. The following results were obtained: (i) In addition to previously described large tumor (T) antigen (94 kilodaltons) and small tumor (t) antigen (19 kilodaltons), a 62-kilodalton polypeptide was immunoprecipitated by SV40 anti-T antiserum from extracts of infected CV-1 and BSC-1 monkey kidney cells and transformed SV3T3 mouse cells. The 94-, 62-, and 19-kilodalton polypeptides were not precipitated with normal serum from extracts of infected cells, and they were not present in extracts of uninfected cells. (ii) The de novo synthesis of the 94-, 62-, and 19-kilodalton tumor antigens was inhibited in CV-1 and BSC-1 cells treated with interferon before infection; total cellular protein synthesis was not significantly affected by interferon treatment. The relative interferon sensitivity of the three polypeptides in lytically infected monkey cells was comparable; by contrast, interferon did not affect their synthesis in transformed mouse cells. (iii) The 62-kilodalton polypeptide was detected in monkey cells infected with the following strains of SV40: tsA30 at both 33 degrees C and 41 degrees C; wt 708, the parent of tsA30; dI 884; and wt 830, the parent of dI 884. The amount of the 62-kilodalton species relative to T antigen was significantly greater in tsA30-infected cells as compared to cells infected with other SV40 strains. (iv) T, t, and 62-kilodalton polypeptides were readily labeled with [(35)S]methionine during a 10-min pulse; in a subsequent chase, the (35)S-labeled 94-kilodalton T antigen was apparently converted to 89- and 84-kilodalton polypeptides but not to either the 62-kilodalton polypeptide species or t antigen. (v) Partial peptide maps suggest that the 62-kilodalton polypeptide and T antigen are closely related. (vi) In addition to the above described 62-kilodalton polypeptide, a 54-kilodalton polypeptide was also detected. However, the 54-kilodalton species appears to be of cellular origin because it was immunoprecipitated with both normal and anti-T antiserum from uninfected and lytically infected cells and from virally transformed cells.

Animals↗
PubMed1979

Mechanism of interferon action: phosphorylation of protein synthesis initiation factor eIF-2 in interferon-treated human cells by a ribosome-associated kinase processing site specificity similar to hemin-regulated rabbit reticulocyte kinase.

The phosphorylation of purified protein synthesis factors catalyzed by protein kinase preparations isolated from interferon-treated human amnion cells was examined. Ribosomal salt-wash fractions prepared from interferon-treated human cells contained a protein kinase that catalyzed the [gamma-(32)P]ATP-mediated phosphorylation of the 38,000-dalton subunit of eukaryotic initiation factor 2 (eIF-2alpha); this kinase activity was significantly enhanced in interferon-treated as compared to untreated cells. The tryptic [(32)P]phosphopeptide pattern obtained for eIF-2alpha phosphorylated by the interferon-mediated human kinase was indistinguishable from the pattern obtained for eIF-2alpha phosphorylated by the hemin-regulated rabbit reticulocyte kinase when analyzed by thin-layer chromatography with three different solvent systems and by high-voltage electrophoresis. O-[(32)P]Phosphoserine was liberated by partial acid hydrolysis from eIF-2alpha phosphorylated by either the human or the rabbit kinase. In addition to the phosphorylation of eIF-2alpha, interferon treatment of human cells enhanced the phosphorylation of two additional ribosome-associated proteins designated P(1) and P(f). The major phosphoester linkage observed for the human, as well as murine, phosphoprotein P(1) was O-phosphoserine. The interferon-mediated phosphorylation of both eIF-2alpha and protein P(1) was dependent upon the presence of RNA with double-stranded character; P(f) phosphorylation was not affected by double-stranded RNA. These results suggest that the interferon-mediated ribosome-associated human protein kinase catalyzes the phosphorylation of eIF-2alpha in a site-specific manner that is apparently identical with the reaction catalyzed by the hemin-regulated rabbit reticulocyte kinase; hence, the phosphorylation of eIF-2 may play a role in regulating the initiation of translation in interferon-treated cells.

Cells, Cultured↗