Anisotropy of lamellar block copolymer grains.

The Wulff construction and the theory of Milner and Morse [Phys. Rev. E 54, 3793 (1996)] were used to calculate the shape of grains formed when a lamellar block copolymer phase is formed by a shallow quench into the ordered state. The calculations show that the grains are ellipsoids of revolution, with an aspect ratio rho=2.37. This value is in reasonable agreement with results of transmission electron microscopy and depolarized light scattering experiments, which indicate that the average value of rho of grains formed during the early stages of the disorder-to-order transition is about 2.0.

Effects of reverse-transcriptase mutations M184V and E89G on simian immunodeficiency virus in Rhesus monkeys.

Mutations in human immunodeficiency virus type 1 reverse-transcriptase codons 89 and 184 confer inhibitor resistance and alter the mutation spectrum of the enzyme. Six macaques were inoculated with wild-type or mutated derivatives (E89G or E89G and M184V) of simian immunodeficiency virus macaque (SIVmac) 239. Five of the infected monkeys maintained high virus loads; the sixth, which was infected with the E89G mutant strain, maintained viremia at a level below the limit of detection. Sequence analysis demonstrated substantial reversion of the E89G mutation in the animals with progressive infection and preservation of this mutation in the animal with controlled infection. A P272S mutation occurred at high frequency in the viruses containing M184V, which did not revert. These results demonstrate that the E89G mutation has a significant negative impact on SIVmac fitness, whereas SIVmac bearing M184V achieved high, sustained virus loads, perhaps with a compensatory effect of the P272S mutation.

Requirements for lymphocyte activation by unusual strains of simian immunodeficiency virus.

When residues 17 and 18 in nef of simian immunodeficiency virus strain SIVmac239 were changed from RQ to YE, the resultant virus was able to replicate in peripheral blood mononuclear cell cultures without prior lymphocyte activation and without the addition of exogenous interleukin-2, caused extensive lymphocyte activation in these cultures, and produced an acute disease in rhesus and pigtail macaques (Z. Du, S. M. Lang, V. G. Sasseville, A. A. Lackner, P. 0. Ilyinskii, M. D. Daniel, J. U. Jung, and R. C. Desrosiers, Cell 82:665-674, 1995). These properties are similar to those of the acutely lethal pathogen SIVpbj14 but dissimilar to those of the parental SIVmac239. We show here that the single change of R to Y at position 17 in nef of SIVmac239 is sufficient to confer the full, unusual phenotype. Conversely, the lymphocyte-activating properties of SIVpbj14 were lost by the single change of Y to R at position 17 of nef. The change of R17F or Q18E in SIVmac239 nef did not confer the unusual in vitro properties. Since SIVpbj14 has a duplication of the NF-kappaB binding sequence in the transcriptional control region, we also constructed and tested strains of SIVmac239/Rl7Y with zero, one, and two NF-kappaB binding elements. We found no difference in the properties of SIVmac239/R17Y, either in cell culture or in vivo, whether zero, one, or two NF-kappaB binding sites were present. Thus, tyrosine at position 17 of nef is absolutely necessary for the unusual phenotype of SIVpbj14 and is sufficient to convert SIVmac239 to a virus with a phenotype like that of SIVpbjl4. Multiple NF-kappaB binding sites are not required for the in vitro properties or for acute disease.

A chimeric human immunodeficiency virus type 1 TAR region which mediates high level trans-activation in both rodent and human cells.

Trans-activation of the HIV-1 LTR by the Tat protein functions by a novel mechanism which involves the direct interaction of the Tat protein and cellular factors with nascently transcribed viral RNA encoding the Tat responsive element (TAR). Rodent cells do not efficiently support HIV-1 Tat activity because of a deficiency of human-specific factor(s). Human chromosome 12 appears to encode one of these Tat cofactors. We have designed chimeric TAR sequences which contain the heterologous RNA sequence derived from the bacteriophage R17 genome which binds to the bacteriophage MS2 coat protein. These chimeric TAR constructs were co-transfected into rodent and human cells with a plasmid encoding a chimeric Tat protein which contains the RNA binding domain of the MS2 coat protein. TAR constructs which contain the MS2 coat protein binding region inserted into the three nucleotide "bulge" region support a high level of trans-activation by Tat-MS2 coat protein chimeras in both human and rodent cells. This result suggests that the human-specific Tat cofactor(s) may act to allow Tat to interact effectively in a ribonucleoprotein complex which includes Tat, cellular factors, and TAR RNA.

5' avian leukosis virus sequences and osteopetrotic potential.

Recombinants of Rous-associated virus-0 and Br21 have been used to localize 5' viral sequences that affect the osteopetrotic potential of avian leukosis viruses. Rous-associated virus-0 is a benign subgroup E virus of endogenous origin that does not cause osteopetrosis. Br21 is a constructed subgroup E virus with high osteopetrotic potential. 5' sequences that affected osteopetrotic potential resided in an 834-bp region near the 5' LTR. Sequence analysis of this region revealed differences between Br21 and RAV-0 in the mRNA leader and codons for MA.

Human chromosome 12 encodes a species-specific factor which increases human immunodeficiency virus type 1 tat-mediated trans activation in rodent cells.

The human immunodeficiency virus type 1 (HIV-1) tat protein functions at a much lower level in rodent cells than in human cells. This species-specific difference in trans activation appears to be due to the lack of a functional homolog of a human cofactor for tat in rodent cells. Using HIV-1 long terminal repeat-driven human growth hormone as a reporter plasmid, we found that the tat-mediated trans activation functions at a level 5- to 20-fold lower in rodent cells than in human cells. Stable rodent-human hybrid cells containing only human chromosome 12 support a dramatically higher degree of trans activation. Thus, human chromosome 12 encodes a species-specific HIV-1 tat cofactor which, at least partially, restores high levels of tat-mediated trans activation. Chromosome 6 also appears to provide an additional factor which enhances HIV-1 tat-mediated trans activation in murine cells.