The effect of cross-links on the conformational dynamics of duplex DNA.

The base pair lifetimes and apparent dissociation constants of a 21 base DNA hairpin and an analog possessing a disulfide cross-link bridging the 3'- and 5'-terminal bases were determined by measuring imino proton exchange rates as a function of exchange catalyst concentration and temperature. A comparison of the lifetimes and apparent dissociation constants for corresponding base pairs of the two hairpins indicates that the cross-link neither increases the number of base pairs involved in fraying nor alters the lifetime, dissociation constant, or the opened structure from which exchange occurs for the base pairs that are not frayed. The cross-link does, however, stabilize the frayed penultimate base pair of the stem duplex. Significantly, it appears that the disulfide cross-link is more effective at preventing fraying of the penultimate base pair than is the 5 base hairpin loop. Because this disulfide cross-link can be incorporated site specifically, and does not adversely affect static or dynamic properties of DNA, it should prove very useful in studies of nucleic acid structure and function.     

Genetic manipulation of plant growth-promoting bacteria to enhance biocontrol of phytopathogens

Plant growth-promoting bacteria (PGPB) control the damage to plants from phytopathogens by a number of different mechanisms including: outcompeting the phytopathogen, physical displacement of the phytopathogen, secretion of siderophores to prevent pathogens in the immediate vicinity from proliferating, synthesis of antibiotics, synthesis of a variety of small molecules that can inhibit phytopathogen growth, production of enzymes that inhibit the phytopathogen and stimulation of the systemic resistance of the plant. Biocontrol PGPB may be improved by genetically engineering them to overexpress one or more of these traits so that strains with several different anti-phytopathogen traits which can act synergistically are created. In engineering these strains it is essential to ensure that the normal functioning of the bacterium is not impaired, i.e., that there is no problem with metabolic load.     

List mania: interpreting microarray results with the L2L server

A new server for interpreting microarray results, list to list(L2L), is described. This tool offers a unique approach to understandthe meaning of microarray results, based on comparing them topreviously identified lists of differentially expressed genes.The usefulness of the server is demonstrated by studying differentialexpression in primary tumours versus metastases in colon cancer.     

Zinc-regulating proteins, ZnT-1, and metallothionein I/II are present in different cell populations in the mouse testis.

Zinc ions play an important role in testis development and spermatogenesis. Thus, nutritional zinc deficiency leads to aberrant testicular development, reduced spermatogenesis, and male sterility. The precise actions of zinc in mediating these functions and the mechanisms by which zinc is itself regulated in the testis, however, have not been adequately elucidated. We have assessed the distribution of the zinc-regulating proteins ZnT-1 and metallothionein I/II (MT I/II) in the mouse seminiferous tubule. Co-labeling for ZnT-1 and MT I/II demonstrated unique patterns of distribution for these proteins, with ZnT-1 present in Sertoli cells in addition to luminal spermatozoa and MT I/II restricted to spermatocytes. These findings were confirmed by dual-label immunofluorescence for ZnT-1 and the Sertoli cell marker, vimentin, and by immunoelectron microscopy. The differential expression patterns of ZnT-1 and MTs support the hypothesis that ZnT-1 and MTs play different roles in the regulation of intracellular zinc in this organ. The specific expression of ZnT-1 in the Sertoli cells, moreover, is consistent with their role in maintaining a nurturing, closely regulated environment for spermatogenesis.     

Lateral hypothalamic lesions and striatal dopamine levels

Rats with bilateral lateral hypothalamic lesions were killed on the third day after surgery and their brains were assayed for tel-diencephalic norepinephrine and striatal dopamine. Lesion-induced weight loss was highly correlated with depletion of striatal dopamine but not with tel-diencephalic norepinephrine. In rats with severe dopamine depletions, the degree of weight loss was related more to the striatum with the highest remaining level of dopamine suggesting that a critical level of dopamine in one striatum may be essential for lateral hypothalamic recovery.     

Stabilization of enzyme activity by incubation in an ethylene atmosphere

Ethylene has a stabilizing effect on the enzymatic activityof yeast alcohol dehydrogenase solutions. The effects of variousconcentrations of ethylene on enzyme activity are demonstrated. (Received August 8, 1972; )