The third hypervariable (V3) domain of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein has been proposed to play an important role in mediating viral entry. Antibodies to the V3 domain block HIV-1 infection but not virus binding to CD4. At the center of the V3 domain is a relatively conserved sequence of amino acids, GPGRA. It has previously been shown that mutation of some of these amino acids reduced the ability of gpl60 expressed on the surface of cells to induce fusion with CD4-bearing cells. In order to analyze the role of V3 domain sequences in mediating HIV entry, we introduced several amino acid substitution mutations in the GPGRA sequence of gpl60 derived from HIV-1 strain HXB2 and in the analogous sequence of strain SF33, GPGKV. Virus was generated by cotransfecting the env constructs and a selectable env-negative HIV vector, HIV-gpt. When complemented with a retrovirus env gene, infectious virus capable of a single round of replication was produced. The viral particles produced were analyzed biochemically for core and envelope proteins and for infectious titer. The transfected envs were also analyzed for ability to bind to CD4 and mediate cell fusion. Several of the amino acid substitutions resulted in moderate to severe decreases in virus infectivity and fusion activity. Envelope glycoprotein assembly onto particles and CD4 binding were not affected. These results provide evidence that V3 sequences are involved in mediating the fusion step of HIV-1 entry.

When the lactose (lac) permease of Escherchia coli is expressed from the lac promoter at relatively low rates, deletion of amino acid residues 2-8 (AT) or 2-9 (A8) from the hydrophilic N terminus has a relatively minor effect on the ability of the permease to catalyze active lactose transport. Activity is essentially abolished, however, and the permease is hardly detected in the membrane when two additional amino acid residues are deleted (A4O), and mutants deleted ofresidues 2-23 (A22) or 2-39 (A38) also exhibit no activity and are not inserted into the membrane. Dramatically, when the defective deletion mutants are overexpressed at high rates via the T7 promoter, A10 and A22 are inserted into the membrane in a stabIeforjnand catalyze active lactose transport in a highly significant manner, whereas A38 is hardly detected in the membrane and exhibits no activity. Interestingly, a fusion protein consisting of A38 and the ompA leader peptide is inserted into the membrane but exhibits no transport activity. The results indicate that the N-terminal hydrophilic domain of lac permease and the N-terminal half of the first putative transmembrane a-helix are not mandatory for either membrane insertion or transport activity.The lactose (lac) permease of Escherichia coli is a hydrophobic, polytopic cytoplasmic membrane protein that. catalyzes the coupled translocation ofp-galactosides and H' with a 1:1 stoichiometry (i.e., symport or cotransport). Encoded by the lacY gene, the permease has been solubilized from the membrane, purified, reconstituted into proteoliposomes, and shown to be solely responsible for f3-galactoside transport (1-3). Based on circular dichroic studies and hydropathy analysis (4), a secondary structure was proposed in which the permease has a short hydrophilic N terminus, 12 transmembrane hydrophobic domains in a-helical configuration connected by hydrophilic loops, and a 17-residue hydrophilic C-terminal tail. Evidence confirming some of the general features of the model and demonstrating that the N and C termini are on the cytoplasmic face ofthe membrane has been obtained from laser Raman (5) and Fourier transform infrared

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The transformation rate of 1,2‐dibromo‐3‐chloropropane (DBCP) was determined in phosphate buffer solution, in groundwater, and in groundwater/aquifer solid slurries from ambient temperatures to 72 °C. From the disappearance data, the apparent Arrhenius constants for DBCP transformation were calculated and found to decrease in Ea with temperature from 19.2 (±2.4) kcal mol−1 in the 55 to 72 °C range to 12.5 (±1.8) kcal mol−1 in the 21 to 55 °C range. Low sorption values were an indication that sorption does not play a major role in the aquifer being studied. No significant difference in the disappearance rates was observed in the buffer solution (corrected for buffer effects) and in groundwater with and without solids added. However, in the phosphate buffer solution, dehydrohalogenation appeared to be the favored transformation process in contrast to the groundwater systems where hydrolysis seemed to predominate. This apparent influence of dissolved constituents or temperature on transformation mechanism or rate may restrain the use of direct extrapolation of data between systems. Applying the transformation data from this study to median field parameters, a DBCP half‐life of 6.1 yr was calculated for typical groundwater conditions in California (pH 7.8 and 21.1 °C).