Identification of acute myeloid leukemia patients with diminished expression of CD13 myeloid transcripts by competitive reverse transcription polymerase chain reaction (RT-PCR).

Normal myeloid cells of monocytic and granulocytic origin express the metallopeptidase cluster of differentiation 13 (CD13) on the surface just as leukemic blasts in most acute myeloid leukemias (AML). A minor percentage of AML patients, however, lack the surface expression of CD13 antigen. To study this difference in CD13 surface expression, specific CD13 mRNA from 44 individuals were quantified by competitive reverse transcription polymerase chain reaction (RT-PCR). Absolute values for CD13 transcripts were normalised against glyceraldehyde-3-phosphate dehydrogenase (GAPDH) transcript levels to control for variations in sample preparation and mRNA degradation. By correlating normalised CD13 transcript levels and CD13 surface expression, a subgroup of AML patients was identified, having simultaneous diminished levels of myeloid CD13 transcripts and surface expression of the corresponding antigen. For this subgroup we suggest CD13/aminopeptidase N (APN) gene expression to be restricted primarily by limited amounts of transcripts. For the majority of AML patients determinants in addition to transcript levels must be involved in regulating CD13/APN gene expression.

Search for a retrovirus in long-term cultured cerebrospinal fluid cells and peripheral blood mononuclear cells from patients with multiple sclerosis.

Long-term peripheral blood mononuclear cell (MNC) cultures stimulated with interleukin 2 (IL-2) or IL-2 + phytohemagglutinin were established from 33 multiple sclerosis (MS) patients, 9 with other neurological diseases (OND), and 24 normal controls (C). Cultures were analysed for growth characteristics, reverse transcriptase (RT) in the culture medium, 2'-5' oligoadenylate synthetase in the cells, and cell morphology. None of these parameters differed in the MS group compared with the OND and C groups. Furthermore, 11 cerebrospinal fluid cell cultures were established without feeder cells. Morphology studies of the cells and RT assays of the supernatants from these cultures were normal. Induction studies by dexamethasone and 2-bromo-5'-deoxyuridine in 2 of these cultures did not reveal any signs of a virus. The significance of these results for the retrovirus hypothesis is discussed.

The physiology of stringent factor (ATP:GTP 3'-diphosphotransferase) in Escherichia coli.

The enzyme ATP:GTP 3'-diphosphotransferase catalyzes the transfer of the beta, gamma-pyrophosphate of ATP to the 3' position of GTP or GDP. The amounts of enzyme were measured in cell extracts of a relA+ strain of E. coli grown at different growth rates between 0.4 and 1.9 generations per hour, using precipitation with specific antibodies to purify the enzyme. The amount of enzyme was found to be a constant fraction of total protein at all growth rates corresponding to about 45 molecules of enzyme per genome equivalent of DNA. The purified enzyme has little catalytic activity by itself but has to be activated either by a complex of 70S ribosomes, mRNA and uncharged tRNA or by a solvent like ethanol at a concentration of about 20%. The kinetic constants of the enzyme for the transfer pyrophosphate from ATP to GTP in the ribosome-activated state were determined. The Vmax was estimated to be 140 mumol/min X mg at 37 degrees C and the S0.5 values for GTP and ATP were 0.35 and 0.53 mM, respectively. The reaction was estimated to have an equilibrium constant of about 300. In the pyrophosphate transfer from ATP to GDP the Vmax was estimated to be 90 mumol/min X mg at 37 degrees C and the S0.5 for GDP as 0.3 mM. During amino acid starvation of a relA+ strain of E. coli the amounts of enzyme and the catalytic capacity of the enzyme are sufficient to maintain the observed ppGpp levels in the cells at all growth rates.