Regulation of human immunodeficiency virus (HIV) gene expression is dependent on specific regulatory regions in the long terminal repeat. These regions include the enhancer, SP1, "TATA," and trans-activating (TAR) regions. In addition, viral regulatory proteins such as tat and rev are important in regulating HIV gene expression. The mechanism of tat activation remains the subject of investigation, but effects at both transcriptional and posttranscriptional levels seem likely. Previous mutagenesis of the tat protein revealed that the amino terminus, the cysteine-rich domain, and the basic domain were all required for complete tat activation. Mutants of other viral trans-acting regulatory proteins, including ElA, tax, and VM65, have been identified that were capable of antagonizing the activity of their corresponding wild-type proteins. We wished to determine whether mutants of the tat protein could be identified that exhibited a similar phenotype.

We have found that the addition of chitosan, a cationic polymer, on whole or skim milk produces destabilization and coagulation of casein micelles that takes place without changes in the milk pH or the stability of most whey proteins. The amount of lipids recovered in the chitosan-casein aggregates was similar or higher than that obtained with rennet or acid precipitation. Approximately 70% of milk Ca2+ (approximately 750 mg/L) was found in the chitosan-induced aggregates, which is 10 and 50% higher than the amounts observed with acid or rennet coagulations, respectively. Purified alpha, beta-, and kappa-caseins were extensively precipitated by different molecular weight chitosans at pH 6.8. The phosphate groups of caseins seem not to be relevant in this interaction because dephosphorylated alpha- and beta-caseins were equally precipitated with chitosans. Analysis by optical microscopy of the chitosan-casein complex reveals that the size of the aggregates increase as the molecular weight of chitosans increase. Hydrophobic and electrostatic interactions particpate in the association and coagulation of casein micelles with chitosans of different molecular weights. The phenomenon is observed over a broad range of temperature (4 to 70 degrees C) with a reduction in the concentration of chitosan needed to precipitate the caseins that parallels a reduction in the viscosity of the chitosan solutions. Taken together, the results indicate that the electrostatic interactions may contribute energetically to the association between the two biopolymers, but the hydrophobicity of the complex would be the key determinant in the overall energetics of the reaction.

Beta-galactoside-binding lectins or galectins are a family of closely related carbohydrate-binding proteins which functions still remain to be elucidated. Several evidence suggest they could play a role in different biological processes, such as cell growth regulation and immunomodulation. In the present study we report that affinity-purified CLL-I (chicken lactose lectin-I), an acidic 16-kDa galectin exhibits specific growth regulatory properties. Con A-stimulated rat spleen mononuclear cells showed a marked dose-dependent growth inhibition upon incubation with the galectin protein. Cell growth arrest was highly prevented by galectin-specific sugars. In addition, biochemical, cytofluorometrical, and morphological evidence are also provided to show that these inhibitory properties are related to a positive control in the apoptotic threshold of spleen mononuclear cells. Flow cytometric analysis showed a dose- and time-dependent increase of cells with hypodiploid DNA content upon exposure to CLL-I. Moreover, cells treated with CLL-I displayed the typical ultrastructural changes compatible with apoptosis, mainly chromatin condensation and margination along the inner surface of the nuclear envelope. Finally, the highly characteristic "ladder" pattern of DNA fragmentation into oligonucleosome-length fragments of approximately 180-200 bp could be found within 6 h of cell culture with CLL-I, mainly in the T cell-enriched population. Induction of apoptosis by a beta-galactoside-binding protein highlights a potentially novel mechanism for regulating the immune response and points to a rational basis for the postulated immunomodulatory properties of this protein family.

The higher HPV DNA detection rate in superficial oral scrapes than in biopsies suggests that accurate epidemiological information on oral HPV infection/oral carcinogenesis depends not only on the DNA detection technique, but also on the tissue/cell sampling procedure.