Molecular dynamics simulations were used to model the response of several double-stranded dodecamers to gradually increasing tension applied to the opposing 3′ ends of the two polynucleotide strands. At forces between 0.80 and 1.45 nN, depending on sequence, the strands separated completely. The separation force for one of the dodecamers studied has been measured and is close to that seen in the simulation. Before strand separation, at forces between 0.065 and 0.090 nN, again depending on sequence, there was an abrupt extension and transition to a novel ladder structure in which bases of one strand were stacked on those of the other strand. Sudden extensions have been observed in very long DNA molecules at forces similar to those seen in the simulations. After the abrupt extension but before strand separation, the ladder structure became more regular, and the phosphate backbones became more linear. Throughout the entire molecular extension, most hydrogen-bonded base pairs remained intact.

Human immunodeficiency virus (HIV) RNA was detected and quantified in the serum of HIV-seropositive individuals using the polymerase chain reaction (PCR) and a nonisotopic enzyme-linked affinity assay. Of 55 HIV-infected patients who were not receiving therapy, serum HIV RNA was detected in 9 of 19 who were asymptomatic, 11 of 16 with AIDS-related complex (ARC), and 18 of 20 with AIDS, with copy numbers ranging from 10(2) to greater than or equal to 5 x 10(4) 200 microliters of serum based on a relationship between absorbance and known copy number of gag gene RNA. Linear regression analysis demonstrated a correlation between infectious titer in 42 patient sera cocultured with donor peripheral blood mononuclear cells (PBMC) and PCR product absorbance (r = .70, P less than .01). Serum HIV RNA detected by PCR also correlated with serum p24 antigen positivity, CD4 counts less than 400/mm3, and the presence of HIV-related symptoms or disease. Quantification of infectious HIV RNA in cell-free serum by PCR may be useful as a marker for for disease progression or in monitoring antiviral therapy.

IPM may have clinical potential as a substitute for platelets in the treatment of bleeding due to thrombocytopenia.

Gene amplification of virus-specific sequences is widely used as a method to detect or confirm human immunodeficiency virus (HIV) infection. In this study we used an enzyme-linked affinity assay to quantify polymerase chain reaction products from whole blood, plasma, and separated mononuclear cells collected in the presence of four common anticoagulants: acid citrate dextrose, sodium EDTA, potassium oxalate, and sodium heparin. Attenuation of the product signal was observed after amplification of nucleic acid extraction from whole blood, washed mononuclear cells, and plasma from specimens collected in sodium heparin. These inhibitory effects on gene amplification could be reversed with heparinase. The addition of as little as 0.05 U of heparin completely inhibited amplification of an HLA-DQa sequence from placental DNA. We conclude that heparin can cause attenuation or inhibition of gene amplification. Acid citrate dextrose and EDTA, which lack inhibitory activity, are the most appropriate anticoagulants for clinical blood samples when polymerase chain reaction amplification is anticipated.

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