Does DNA compute? Molecular computing.

The demonstration that DNA molecules can act as parallel processors to solve hard problems has excited interest in the possibility of developing molecular computers based on recombinant DNA techniques.

Rat serum amyloid P component. Analysis of cDNA sequence and gene expression.

cDNA clones for rat serum amyloid P component (SAP) were isolated, and the derived amino acid sequence for pre-SAP was determined from the complete nucleotide sequence. Rat SAP is encoded by approximately 1 kb of mRNA, and the mature SAP protein is predicted to be 208 amino acids long. An increase in hepatic mRNA levels for rat SAP was found after administration of lipopolysaccharide, and SAP mRNA levels in livers of unstimulated male rats were lower than in hepatic RNA from female rats.

Scholarship in teaching and best evidence medical education: synergy for teaching and learning.

Medical education has lagged behind research and clinical care in developing a value system and social construct that promotes and stimulates the open discussion of the state of the art in teaching among teachers. The recent development of best evidence medical education (BEME) in Europe and the renewed attention to the concept of scholarship in North America provide a conceptual and strategic approach for enhancing the educational enterprise in the health professions. The similarities and differences between BEME and an approach to Scholarship in Teaching developed by a subcommittee of the Group on Educational Affairs of the Association of American Medical Colleges is examined. Combining these two approaches to medical teaching can maximize the potential for advancing the science and art of medical education.

Target size of the ryanodine receptor from junctional terminal cisternae of sarcoplasmic reticulum.

Target inactivation analysis was carried out on the ryanodine receptor. This receptor recently has been implicated as the channel involved in the calcium release process in excitation-contraction coupling and was localized to the junctional terminal cisternae of sarcoplasmic reticulum from skeletal muscle [Fleischer, S., Ogunbunmi, E. M., Dixon, M. C., & Fleer, E.A.M. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7256-7259]. Irradiation of the junctional terminal cisternae resulted in an exponential decrease in ryanodine binding with radiation dose, thereby consistent with target theory. The target molecular weight was found to be 138,000 +/- 21,000, i.e., smaller than the polypeptide that binds ryanodine. The calcium pump protein in the same membrane preparation served as an internal control to validate the methodology.

Positive cooperativity of ryanodine binding to the calcium release channel of sarcoplasmic reticulum from heart and skeletal muscle.

Ryanodine is a specific ligand for the calcium release channel which mediates calcium release in excitation-contraction coupling in muscle. In this study, ryanodine binding in sarcoplasmic reticulum from heart muscle and skeletal muscle is further compared and correlated with function. The new findings include the following: (1) Two types of binding, high affinity (KD1 approximately 5-10 nM) and low affinity (KD2 approximately 3 microM), can now be discerned for the skeletal muscle receptor. KD1 is approximately the same as and KD2 of similar magnitude to that previously reported for heart. (2) The dissociation rates for the high-affinity binding have been directly measured for both heart and skeletal muscle (t1/2 approximately 30-40 min). These rates are more rapid than previously reported (t1/2 approximately 14 h). (3) KD1's obtained from the ratio of the dissociation and association rate constants agree with the dissociation constant measured by equilibrium binding Scatchard analysis. (4) Ryanodine binding to the low-affinity site can be correlated with a decrease in the dissociation rate constant (k-1) of the high-affinity site, and thereby in the apparent dissociation constant (KD1). The inhibition constant (KI) for inhibiting the high-affinity off rate obtained from a double-reciprocal plot of the change in off rate vs [ryanodine] is practically the same in heart (0.66 microM) and skeletal muscle (0.64 microM) and in the range of the KD2. The binding of cold ryanodine to the low-affinity site appears to lock the bound [3H]ryanodine onto the high-affinity site rather than to exchange with it. Thus, in this sense, the ryanodine receptor exhibits "positive cooperativity".(ABSTRACT TRUNCATED AT 250 WORDS)

A mouse knock-in model exposes sequential proteolytic pathways that regulate p27Kip1 in G1 and S phase.

The protein p27Kip1 is an inhibitor of cell division. An increase in p27 causes proliferating cells to exit from the cell cycle, and a decrease in p27 is necessary for quiescent cells to resume division. Abnormally low amounts of p27 are associated with pathological states of excessive cell proliferation, especially cancers. In normal and tumour cells, p27 is regulated primarily at the level of translation and protein turnover. Phosphorylation of p27 on threonine 187 (T187) by cyclin-dependent kinase 2 (Cdk2) is thought to initiate the major pathway for p27 proteolysis. To critically test the importance of this pathway in vivo, we replaced the murine p27 gene with one that encoded alanine instead of threonine at position 187 (p27T187A). Here we show that cells expressing p27T187A were unable to downregulate p27 during the S and G2 phases of the cell cycle, but that this had a surprisingly modest effect on cell proliferation both in vitro and in vivo. Our efforts to explain this unexpected result led to the discovery of a second proteolytic pathway for controlling p27, one that is activated by mitogens and degrades p27 exclusively during G1.

Comparison of the calcium release channel of cardiac and skeletal muscle sarcoplasmic reticulum by target inactivation analysis.

The calcium release channel of sarcoplasmic reticulum which triggers muscle contraction in excitation-contraction coupling has recently been isolated. The channel has been found to be morphologically identical with the feet structures of the junctional face membrane of terminal cisternae and consists of an oligomer of a unique high molecular weight polypeptide. In this study, we compare the target size of the calcium release channel from heart and skeletal muscle using target inactivation analysis. The target molecular weights of the calcium release channel estimated by measuring ryanodine binding after irradiation are similar for heart (139,000) and skeletal muscle (143,000) and are smaller than the monomeric unit (estimated to be about 360,000). The target size, estimated by measuring polypeptide remaining after irradiation, was essentially the same for heart and skeletal muscle, 1,061,000 and 1,070,000, respectively, indicating an oligomeric association of protomers. Thus, the calcium release channel of both cardiac and skeletal muscle reacts uniquely with regard to target inactivation analysis in that (1) the size by ryanodine binding is smaller than the monomeric unit and (2) a single hit leads to destruction of more than one polypeptide, by measuring polypeptide remaining. Our target inactivation analysis studies indicate that heart and skeletal muscle receptors are structurally very similar.