Partial purification and characterization of the reverse transcriptase of the simian immunodeficiency virus TYO-7 isolated from an African green monkey

Expression and characterization of the reverse transcriptase enzyme from type 1 human immunodeficiency virus using different baculoviral vector systems

To produce the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) in amounts required to study its structure and function, the p66 enzyme subunit was expressed using two different baculovirus vectors in Sf158 insect host cells. Both vectors permitted an efficient HIV-1 RT expression. The resulting products were purified up to 90% homogeneity, characterized, and investigated for their susceptibility to digestion with various proteases. The recombinant baculoviral RT obtained with the pAc373 expression vector was purified as a p66/p60 heterodimer. The recombinant His-RT was expressed with the pBlueBacHis vector. Thereby, the protein was tagged with an N-terminal hexahistidine peptide and it was purified as a p70/p70 homodimer. The two enzymes differed in their specific activity, kinetic properties, and in vitro activation by viral and non-viral proteases. The recombinant His-RT exhibited a lower specific activity than the recombinant RT. The latter yielded enzyme activities as high as an Escherichia coli-expressed RT. Removal of the hexahistidine tag from the recombinant His-RT by digestion with enterokinase resulted in a complete loss of enzyme activity. Thus, the hexahistidine tag might be an intrinsic part of the active recombinant His-RT.

Chemical modifications of aminonaphthalenesulfonic acid derivatives increase effectivity and specificity of reverse transcriptase inhibition and change mode of action of reverse transcriptase and DNA polymerase alpha inhibition

The reverse transcriptase (RT) inhibition and the specificity of 15 aminonaphthalenesulfonic acid derivatives were examined with RT of a simian immunodeficiency virus derived from an African green monkey (SIVagmTYO-7). The two compounds with the strongest RT inhibition (NF415) or the highest specificity (NF345), together with suramin, were evaluated against polymerase alpha-primase complex from calf thymus. We have also compared the kinetics of inhibition of the viral and the cellular polymerase by these three compounds. While RT inhibition followed a mixed competitive and non-competitive mechanism, inhibition of the DNA polymerase alpha was competitive for suramin and non-competitive for NF415 and NF345. Certain structural characteristics appeared to be common for specific RT inhibitors.

Activity gel and activity blotting methods for detecting DNA-modifying (repair) enzymes

Zymographical methods (activity gel, overlay gel, activity blot and activity blotting) for detecting DNA-modifying (repair) enzymes are reviewed. Emphasis is put on the novel activity blotting method in which DNA repair enzymes electrophoresed on a gel are blotted and detected on a damaged DNA-fixed nylon membrane. Its practical procedures, including a non-radioactive detection procedure, and representative results are also described.

Biochemical and immunological characterization of micellar complexes of the envelope glycoprotein of a simian immunodeficiency virus isolated from an African green monkey

The external envelope glycoprotein gp130 of a simian immunodeficiency virus isolated from an African green monkey (SIVagmTYO-7) was purified as micellar complexes. The molecular weight of the gp130 micelles was about 700 K. On electron microscopy, the micelles appeared as spherical particles with a diameter of 15 to 20 nm. Such aggregates consisted of about 4 to 5 gp130 monomers. Hyperimmune sera raised in rabbits and rhesus monkeys against these gp130 micelles exhibited titers between 10(5) and 10(6). Such sera inhibit the CD4 binding of gp130 and neutralize SIVagmTYO-7 and SIVmac251 but not HIV-2ben.

Characterization of the endogenous reverse transcriptase reaction products of SIVagmTYO-7, a simian immunodeficiency virus isolated from an African green monkey

The products of the endogenous reverse transcriptase reaction of SIVagmTYO-7 were characterized after the reaction conditions had been optimized. The major reaction product in the presence of actinomycin D and oligo(dT) was a DNA with a size of 300 bases. Without actinomycin D two additional reaction products with 600 or 700 bases appeared. The 300 base product was identified as the (-)strong-stop DNA, whereas the 700 base product is the (+)strong-stop DNA. The 600 base product appeared only after oligo(dT) priming. The (-)strong-stop DNA hybridized specifically with a 9 kb RNA found in virus particles and three RNA species of 1.8, 4.8 and 9 kb isolated from SIVagmTYO-7 infected cells.

Detection of viral surface antigens on HIV-2ben infected human tumor cell lines by flow cytometry

The human monocytic cell line U-937 clone 2 and two T-cell lines CEM and MOLT-4 clone 8 were infected with HIV-2ben, a recent isolate of HIV-2. Infection and subsequent antigen expression on the cell surface was monitored by flow cytometry using a rabbit-anti-serum against tween-ether-treated HIV-2ben and a fluorescein-isothiocyanate-conjugated IgG against rabbit-IgG. The sensitivity of the three cell lines to infection with HIV-2ben correlated with the percentages of CD4-expressing cells but not with the levels of CD4-expression on the cell. The appearance of viral surface antigens preceded the formation of syncytia and correlated closely with the infecting virus dose. After 1-2 weeks in culture, 20-85% of the cells of each line expressed viral surface antigens. The variation depended on the cell type and cell culture conditions. The MOLT-4 clone 8 and the U-937 clone 2 cells died around 10 or 20 days, respectively, after HIV-2ben infection. Only HIV-2ben infected CEM cells grew permanently. Flow cytometry was an appropriate method to monitor the expression of viral proteins on the cell surface of HIV-infected cell lines. Flow cytometry proved to be more sensitive than determination of RT activity in supernatants of HIV-infected cells and more precise than light microscopy examinations.

Fidelity of reverse transcriptase of the simian immunodeficiency virus from African green monkey

The in vitro fidelity of highly purified recombinant reverse transcriptase from simian immunodeficiency virus of African green monkeys (SIVagm) was determined. By using the phi X174am16 reversion assay an overall error rate of 1/19,000 was determined. This is 2.4-fold higher than the overall accuracy of purified recombinant HIV-1 reverse transcriptase, measured in parallel. The evaluation of error frequencies from nucleotide pool bias studies suggest an even higher accuracy for the SIVagm-derived reverse transcriptase. T:dGMP mismatches were formed most frequently with an error rate of 1/155,000, followed by G:dGMP (1/230,000), A:dGMP (1/315,000), G:dAMP (1/340,000), T:dCMP (1/540,000), T:dTMP (1/790,000), and A:dCMP (1/1,050,000) mispairs. Thus, according to pool bias effects and depending on the mismatch under consideration SIVagm reverse transcriptase appears to be 2 to 20-fold more accurate than the homologous enzyme from the human immunodeficiency virus type 1. This higher accuracy is not due to a co-purifying exonuclaease activity. Like the enzyme from HIV-1, the simian monkey-derived enzyme was found to be devoid of a proofreading 3' to 5' exonuclease.