High-risk sexual behavior at a midwestern university: a confirmatory survey

According to a 1991 study of sexual behavior based on a random sample of heterosexual undergraduates at a Midwestern university, 80% of the males and 73% of the females had experienced vaginal or anal intercourse. The average age at first vaginal intercourse was 17.2 years for both sexes. Seventeen percent of the sexually experienced males and 18% of the sexually experienced females had engaged in heterosexual anal intercourse; among these respondents, the average age at first anal intercourse was 20.3 for males and 19.1 for females. Although less than four years, on average, had elapsed since the respondents had first had vaginal intercourse, males reported an average of 8.0 lifetime vaginal-sex partners and females reported an average of 6.1. Overall, the findings from this random sample of students are similar to those from a 1988 convenience sample of the same college population.     

Involvement of spicules in the formation of vaccinia virus envelopes elucidated by a conditional lethal mutant

The envelope of immature vaccinia virions consists of a lipoprotein bilayer upon which a precise curvature is imposed by acquisition of an external scaffold of spicules. Self-assembly of this tegument was examined employing our ts 6757 mutant, which induces accumulation of immature envelopes at the restrictive temperature. With ts 6757 the envelope bilayers were also assembled into an alternative membrane configuration in the form of flexible cylinders or tubes of uniform width, lacking the spicule coat. Such tubes became extensions of or were continuous with the spherical virion envelopes. The approximately 65 kDa spicule protein, L65, product of gene D13L on the HindIII map, generally designated as a late protein, was expressed as an early function in presence of hydroxyurea, an inhibitor which entirely blocked vaccinia DNA synthesis without stopping assembly of immature envelopes. Labeling of thin sections by immunogold for electron microscopy demonstrated that L65 is present at the surface of immature virions, consistent with the position of spicules on envelopes. Transiency of the spicule scaffold was documented by (a) absence of L65 from intracellular mature virions (IMV) and (b) rapid turnover of L65 during ts 6757 virus replication at the permissive temperature but conservation of this protein at restrictive temperature, as demonstrated in pulse-chase experiments. Time-related decrease in MW of L65 to a smaller polypeptide is interpreted as evidence suggesting that the spicules attached to the envelope are assembled from a higher MW precursor.     

Visceral leishmaniasis: II. Histiocyte ultrastructure in bone marrow associated with low level of parasitaemia and mimicking malignant histiocytosis

The ultrastructural features of histiocytes in the bone marrow (BM) were studied in a febrile, splenomegalic and pancytopenic Sudanese patient who was diagnosed by one of us as visceral leishmaniasis (VL) associated with low level of parasitaemia and mimicking malignant histiocytosis (MH). Serial thick (STS) and ultrathin (SUT) sections showed that the BM was hypercellular and markedly infiltrated by large histiocytes with prominent phagocytosis. A thorough examination of various ST and UT section revealed only a single, typical Leishman-Donovan body. At transmission electron microscopy (TEM) level, two principal types of histiocytic cells were identified: Type I, subdivided into two subtypes, were actively phagocytic histiocytes (PH) with large digestive vacuoles and primary lysosomes; type II were nonphagocytic histiocytes (nPH) with primary lysosomes only. The rate of PH to nPH ws 7:2 in plastic STS. The interaction between the PH and ingested cells is described. Both types of cell were morphologically similar to previously described malignant histiocytic cells. However, this study showed a better characterization of PH during VL.     

pH titration of native and unfolded beta-trypsin: evaluation of the delta delta G0 titration and the carboxyl pK values

The stabilizing free energy of beta-trypsin was determined by hydrogen ion titration. In the pH range from 3.0 to 7.0, the change in free energy difference for the stabilization of the native protein relative to the unfolded one (delta delta G0 titration) was 9.51 +/- 0.06 kcal/mol. An isoelectric point of 10.0 was determined, allowing us to calculate the Tanford and Kirkwood electrostatic factor w. This factor presented a nonlinear behavior and indicated more than one type of titratable carboxyl groups in beta-trypsin. In fact, one class of carboxyl group with a pK = 3.91 +/- 0.01 and another one with a pK = 4.63 +/- 0.03 were also found by hydrogen ion titration of the protein in the folded state.