Conversion of 5′-Methylthioadenosine into S-adenosylmethionine by yeast cells

5′-Methylthio[U-¹⁴C]adenosine was used as a culture supplement for Candida utilitis. The resulting S-adenosylmethionine was hydrolyzed into its structural components. Virtually none of the label of the pentose was found in the carbohydrate part of the intracellular S-adenosylmethionine. Much of it was present in the four-carbon chain of the methionine part of the sulfonium compound. The U-¹⁴C)-labeled adenine of 5′-methylthio[U-¹⁴C]adenosine did not contribute to the labeling of the amino acid component of the sulfonium compound.     

Cytologische Untersuchungen am Gehirn alternder Bienen und die Frage nach dem Alterstod

Ohne Zusammenfassung     

A homeobox-containing marker of posterior neural differentiation shows the importance of predetermination in neural induction

A homeobox sequence has been used to isolate a new Xenopus cDNA, named XIHbox6. A short probe from this gene serves as an early marker of posterior neural differentiation in the Xenopus nervous system. The gene recognized by this cDNA sequence is first transcribed at the late gastrula stage and solely in the posterior neural cells. The gene is expressed when ectodermal and mesodermal tissues of an early gastrula are placed in contact, but not by either tissue cultured on its own. However, gene expression is most easily inducible in ectoderm from the dorsal region, i.e., in ectoderm normally destined to form neural structures. This establishes the principle, in contrast to previous belief, that the induction of the embryonic nervous system involves a predisposition of the ectoderm and does not depend entirely on an interaction with inducing mesoderm.     

Influence of chain shortening on the inhibitor properties of hirudin and eglin c

To find out minimal sizes of the proteinase inhibitor proteins hirudin and eglin necessary for their biological activity the inhibitors were incubated with exopeptidases. From the incubation mixtures shortened derivatives were isolated and characterized. Eglin c can be N-terminally shortened by up to 6 amino-acid residues without any loss of affinity towards chymotrypsin. The complex of thrombin with hirudin lacking 3 C-terminal amino-acid residues showed a 15-20-fold increased Ki value as found previously for desulfato-hirudin and desulfato-hirudin shortened by 2 amino-acid residues. Obviously, the C-terminal part of the hirudin molecule has a positive influence on its affinity to thrombin.     

Rete testis fluid (RTF) proteins: purification and characterization of RTF albumin

A major 68-kDa protein in ram rete testis fluid (RTF) is shown to be chemically and immunologically indistinguishable from albumin in ovine serum. Data obtained with two-dimensional gel electrophoresis of RTF demonstrate the presence of additional proteins with a molecular mass of 68 kDa that do not react with antisera against sheep serum albumin. Biochemical characteristics of albumin preparations isolated by immunoaffinity chromatography from ovine serum and from RTF were compared. Albumin from both sources had the same apparent molecular mass of 68 kDa, the same isoelectric point of approximately 4.2, and neither bound specifically to Concanavalin A. Analysis of tryptic peptide maps, obtained with reverse-phase high-pressure liquid chromatography, indicated no significant differences between digests of the two purified albumin preparations. Results indicate that RTF albumin and serum albumin are the same protein, which implies that RTF albumin may originate from serum. Albumin levels in RTF, collected from different rams and measured by radioimmunoassay, varied between 46 and 164 micrograms/ml, constituting between 11 and 17% of total RTF protein, while albumin levels in sheep plasma were 40,000 micrograms/ml. The protein composition of RTF is discussed in relation to the relative amounts of various components contributed by testis cells and the amounts derived from serum.     

The effect of sucrose on the levels of abscisic acid, indoleacetic acid and zeatin/zeatin riboside in wheat ears growing in liquid culture

The influence of a varied sucrose supply on grain size and hormonal contents of detached wheat ears ( Triticwn aestivum L. cv. Schirokko) was investigated throughout grain development. In ears led limited amounts, or no sucrose, grain weights in both proximal and distal grain positions of the ear were reduced. Radioimmunoassay for abscisic acid, indoleacetic acid and zeatin/zeatin riboside showed that the changes in the levels of these hormones in grains and bracts were comparable to intact ears when detached ears were well supplied with sucrose. Under conditions of limited sucrose supply, higher abscisic acid levels in the distal and proximal grains of detached ears were found compared to ears supplied with adequate sucrose. Limiting sucrose supply to the ear did not alter the levels of indoleacetic acid or zeatin/zeatin riboside in either the grains or bracts of detached ears.     

Efficient oligonucleotide-directed construction of mutations in expression vectors by the gapped duplex DNA method using alternating selectable markers.

An efficient method for the construction of multiple mutations in a sequential manner is described. It is based on the gapped duplex DNA approach to oligonucleotide-directed mutagenesis (Kramer et al. 1984, Nucl. Acids Res. 12, 9441-9456) and a set of newly constructed phasmid vectors. These are characterized by the following features. Presence of the phage fl replication origin permits ready conversion to the single stranded DNA form. An amber mutation within, alternatively, the bla or cat gene provides a means for ready selection of the strand into which the mutagenic oligonucleotide has been incorporated. By means of the alternating antibiotic resistance markers any number of mutations can be constructed in consecutive rounds of mutagenesis. The optional presence of gene expression signals allows the direct overproduction of structurally altered proteins without re-cloning. Both the mutagenesis and expression aspects were tested using the lacZ gene as a model.