Rapid turnover of adenovirus E1A is determined through a co-translational mechanism that requires an aminoterminal domain.

The product of the adenovirus E1A 13S mRNA can both stimulate and repress the expression of certain viral and cellular genes. As with several other regulatory proteins, E1A has a short half-life, approximately 40 min. Although this short half-life is observed in cells expressing the E1A gene, it is not the case with cells injected with E1A protein, where its half-life is very long, generally greater than 15 h. We have sought to reconcile these apparent differences in E1A stability. Using Xenopus oocytes, we find that E1A exhibits its characteristic short half-life when it is synthesized from injected mRNA while it has a very long half-life when it is injected as a protein synthesized originally in Escherichia coli or reticulocyte lysates. In order to delineate the amino acids responsible for rapid E1A turnover, several deletion mRNAs were constructed, injected into oocytes, and E1A half-life determined. Carboxyl-terminal deletions and an internal deletion of residues 38-86 failed to increase the half-life of E1A. In contrast, amino-terminal deletions of 70 and 14 residues resulted in very stable E1A proteins (t1/2 greater than 20 h). Furthermore, deletion of the second amino acid, an arginine, resulted in a stable E1A protein. The amino-terminal region of E1A was able to induce the rapid turnover of a normally stable protein, beta-globin, in oocytes injected with an E1A-globin chimeric mRNA. This E1A-induced instability of globin was abolished, however, when the protein was first synthesized in reticulocyte lysates and then injected into oocytes. The amino-terminal region of E1A is also important in governing halflife in adenovirus-infected HeLa cells. These results demonstrate that the half-life of E1A is established cotranslationally through a mechanism involving sequences within the amino-terminal 37 residues.     

The role of beta-hydroxyaspartate and adjacent carboxylate residues in the first EGF domain of human factor IX.

beta-Hydroxyaspartic acid is a post-translationally modified amino acid found in a number of plasma proteins in a domain homologous to epidermal growth factor. Its presence can be correlated with a high affinity Ca2+ binding site, with a dissociation constant of 10-100 microM. We describe a system for the expression of human coagulation factor IX in dog kidney cells in tissue culture, in which the post-translational modifications and the biochemical activity are indistinguishable from factor IX synthesized in vivo. This system has been used to express eight different point mutations of human factor IX in the first epidermal growth factor domain in order to study the role of beta-hydroxyaspartate at residue 64, and the adjacent carboxylate residues at positions 47, 49 and 78. We conclude that this domain is essential for factor IX function and suggest that Ca2+ binds to carboxylate ions in this domain and stabilizes a conformation necessary for the interaction of factor IXa with factor X, factor VIII and phospholipid in the next step of the clotting cascade.     

A water-soluble fraction from adult bone stimulates the differentiation of cartilage in explants of embryonic muscle

A water-soluble fraction of a 4 M guanidine HCl extract of demineralized adult bovine bone stimulated the differentiation of cartilage in explants of minced skeletal muscle from embryonic chick legs; cartilage was also induced by a semipurified protein preparation. Cartilage could be identified in treated cultures at 1 week with muscle from day-9 embryos, not before 2 weeks with muscle from day-12 embryos, and not before 3 weeks with muscle from day-19 embryos. The ability to respond to this water-soluble fraction by exhibiting cartilage differentiation was dose-dependent, but not confined to any particular muscle region of the day-12 embryonic leg. These observations indicate that bone-derived soluble chondroinductive agents act on cells in minced embryonic muscle preparations. The induction of cartilage is dependent upon the accessibility of the responding cells to the agents, on the concentration of inductive agents, and on the developmental age of the responsive tissue.     

Gender difference in the relationship of performance in the handgrip and standing long jump tests to lean limb volume in young adults

Groups of young, adult males and females performed the handgrip and standing long jump tests. Their total forearm and leg volumes were calculated from a series of circumference and length measurements, and the lean volumes (bone + muscle) calculated by taking the skinfold thickness into consideration. In the handgrip, the mean female performance was 298 N compared with 496 N for the males. In the standing long jump, mean performance expressed as distance x body mass was 87.3 kg.m for females compared with 137.7 kg.m for males. These superior performances of males could simply reflect their greater muscle mass, as the mean lean volumes of female and male limbs respectively were 0.54 l and 0.89 l for forearms, and 11.82 l and 14.82 l for the two legs. However, when the performances of males and females were grouped by lean limb volume, it was found that while in both tests there were linear relationships, males and females did not share a common line. In both tests the male relationship was at a higher level than the female; therefore, for a given lean volume, the male performance was significantly superior to that of the female. The gender difference found in this study has not been seen in other studies in which the performance of skeletal muscle has been related to the cross-sectional area of the active muscles and the possible reasons for the differences are considered.     

Taking care of patients--does it matter whether the physician is a woman?

Researchers have recently begun to compare male and female physicians'' attitudes toward patients, medical knowledge, and practice styles. Although women start medical school with more "humanistic views," the conservative effect of medical socialization on both male and female students attenuates these differences. While some studies suggested that men are more scientifically knowledgeable, recent studies showed no significant differences in physicians'' medical knowledge. Male and female physicians also had comparable diagnostic and therapeutic behavior. In the intimate world of physicians and patients, however, there were notable differences. Women physicians seemed better able to communicate sensitivity and caring to patients, which may account for the common perception that women are more caring and empathic physicians. Medical educators may wish to study more closely female physicians'' communication styles to identify these behaviors and inculcate them into all physicians.