GaP_(1-x)N_x混晶(x=0.24%～3.1%)发光复合机制的研究

利用变温光致发光(PL)谱研究了一系列GaP1-xNx混晶的发光复合机制.GaP1-xNx混晶的PL谱从低组分的NN对束缚激子及其声子伴线到高组分杂质带发光的特征,表现出明显的带隙降低的趋势.测量结果显示,在组分x≥0.24%的样品的发光谱中NN1能量之下已经开始出现几个新的束缚态,在低组分的混晶中,只存在一种激活能,仍然保持有束缚激子的特征;而在高组分样品(x≥0.81%)中存在两种激活能.高组分样品一方面仍保留有束缚激子的特征,另一方面也表现出新的发光机制.     

Linkage of Mls genes to endogenous mammary tumour viruses of inbred mice.

T cells that recognize self antigen are clonally deleted in the thymus--a maturation process that occurs in the context of histocompatibility molecules and the T-cell receptor. The minor lymphocyte stimulation antigens (Mls) effect these deletions through interactions with the V beta portion of the T-cell receptor, thus mimicking bacterial 'superantigens'. Intrigued by the fact that each known Mls gene maps to the same chromosomal region as an endogenous mouse mammary tumour virus (Mtv), we reevaluated the linkage relationships between the two gene families. Here we report perfect concordance in inbred and recombinant inbred mice between the presence of four Mtv proviruses with the expression of Mls gene products. These data suggest a general model in which mammary tumour virus gene products themselves are the ligands that shape a considerable portion of the immunological repertoire of common laboratory mice.     

Metallurgy, the Father of Materials Science

The BeginningsThe English- language phrase materials science andengineering ( MSE) emerged at an unknown timeand place in the United States of America in theearly 1 95 0 s.One suggestion is that it,and theconcept it denotes,arose out of sustaineddiscussio…     

Cloning and expression of the essential gene for poly(A) polymerase from S. cerevisiae.

Poly(A) polymerase is essential for the maturation of messenger RNA, adding tracts of adenosine residues to the 3' end of precursor RNA generated by endonucleolytic cleavage. This mechanism of mRNA 3' processing seems to be similar in yeast and in higher eucaryotes, although there are differences in the recognition signals in the pre-mRNA. Here we describe the cloning of the gene for yeast poly(A) polymerase. The enzyme is encoded by a single and essential gene located near the centromere on the left arm of chromosome 11. Poly(A) polymerase purified from recombinant Escherichia coli has the same physical and biochemical properties as the yeast enzyme. The yeast poly(A) polymerase shares features of sequence with its mammalian homologue.     

A recycling pathway between the endoplasmic reticulum and the Golgi apparatus for retention of unassembled MHC class I molecules

Assembly of class I major histocompatibility complex (MHC) molecules involves the interaction of two distinct polypeptides (the heavy and light chains) with peptide antigen. Cell lines synthesizing both chains but expressing low levels of MHC class I molecules on their surface as a result of a failure in assembly and transport have been identified. We now report that although the apparent steady-state distribution in these cells of class I molecules is in the endoplasmic reticulum (ER), the molecules in fact are recycled between the ER and Golgi, rather than retained in the ER. This explains the failure of class I molecules to negotiate the secretory pathway. Class I molecules do not seem to be modified by Golgi enzymes, suggesting that the proteins do not reach the Golgi apparatus during recycling. But morphological and subcellular fractionation evidence indicates that they pass through the cis Golgi or a Golgi-associated organelle, which we postulate to be the recycling organelle. This compartment, which we call the 'cis-Golgi network', would thereby be a sorting organelle that selects proteins for return to the ER.     

Countercurrent chromatography meets MS

Interfacing countercurrent chromatography with thermospray mass spectrometry provides a new analytical tool for detecting nonvolatile, hydrophilic or thermally unstable bioactive natural products.     

A superantigen encoded in the open reading frame of the 3' long terminal repeat of mouse mammary tumour virus.

Mice express a collection of superantigens, which bind to class II major histocompatibility proteins and interact with T cells bearing particular V beta chains as part of their alpha beta receptors. These superantigens have been suggested to be encoded by exogenous or endogenous mouse mammary tumour viruses. One such superantigen is now shown to be encoded in the open reading frame of the long terminal repeat of a mammary tumour virus, a gene of previously unknown function.     

Comparison of counterimmunoelectrophoresis (CIE), latex agglutination (LA) and staphylococcal coagglutination (COAG) in pneumococcal antigen detection in vitro

CIE was compared to agglutination assays employing commercial kits (Directigen, Phadebact), as well as our own LA and COAG reagents, in detection of pneumococcal capsular polysaccharide (PCP) antigens in vitro. Directigen provided the most sensitive assay. CIE was of comparable sensitivity except for PCP antigen types 7 and 14.