Regulation of septum formation in Aspergillus nidulans by a DNA damage checkpoint pathway.

In Aspergillus nidulans, germinating conidia undergo multiple rounds of nuclear division before the formation of the first septum. Previous characterization of temperature-sensitive sepB and sepJ mutations showed that although they block septation, they also cause moderate defects in chromosomal DNA metabolism. Results presented here demonstrate that a variety of other perturbations of chromosomal DNA metabolism also delay septum formation, suggesting that this is a general cellular response to the presence of sublethal DNA damage. Genetic evidence is provided that suggests that high levels of cyclin-dependent kinase (cdk) activity are required for septation in A. nidulans. Consistent with this notion, the inhibition of septum formation triggered by defects in chromosomal DNA metabolism depends upon Tyr-15 phosphorylation of the mitotic cdk p34nimX. Moreover, this response also requires elements of the DNA damage checkpoint pathway. A model is proposed that suggests that the DNA damage checkpoint response represents one of multiple sensory inputs that modulates p34nimX activity to control the timing of septum formation.     

Principles and pitfalls in designing site-directed peptide ligands

An immunoglobulin light chain dimer with a large generic binding cavity was used as a host molecule for designing a series of peptide guest ligands. In a screening procedure peptides coupled to solid supports were systematically tested for binding activity by enzyme linked immunosorbent assays (ELISA). Key members of the binding series were synthesized in milligram quantities and diffused into crystals of the host molecule for X-ray analyses. These peptides were incrementally increased in size and affinity until they nearly filled the cavity. Progressive changes in binding patterns were mapped by comparisons of crystallo-graphically refined structures of 14 peptide–protein complexes at 2.7 Å resolution. These comparisons led to guidelines for ligand design and also suggested ways to modify previously established binding patterns. By manipulating equilibria involving histidine, for example, it was possible to abolish one important intramolecular interaction of the bound ligand and substitute another. These events triggered a change inconformation of the ligand from a compact to an extended form and a comprehensive change in the mode of binding to the protein. In dipeptides of histidine and proline, protonation of both imidazolium nitrogen atoms was used to program anend-to-end reversal of the direction in which the ligand was inserted into the binding cavity. Peptides cocrystallized with proteins produced complexes somewhat different in structure from those in which ligandswere diffused into preexisting crystals. In sucha large and malleable cavity, space utilization was thus different when a ligand was introduced before the imposition of crystal packing restraints. © 1993 Wiley-Liss, Inc.     

Effects of hypophysectomy and immobilization stress on S-adenosylmethionine levels in rat adrenal glands

Rat adrenal S-adenosylmethionine (SAM) levels and phenylethanolamine-N-methyltransferase (PNMT) activity were measured under conditions of hypophysectomy and stress. A new dual-label radioenzymatic assay for SAM is presented which eliminates problems found to exist with previous methods. Strain-specific differences in both PNMT and SAM were found, as well as sex differences in SAM levels. Immobilization stress resulted in an increase in adrenal SAM and PNMT activity, while hypophysectomy decreased both. The distribution of SAM between cortex and medulla did not change with either hypophysectomy or stress. Hypophysectomized Fisher rats were found to be capable of increasing PNMT activity in the absence of increased SAM levels.     

On the directional orientation of female presents inMacaca fascicularis

The directional orientation of female presents in a captive group of long-tailed macaques (Macaca fascicularis) is markedly dependent upon the sex of the potential recipient. Females present in the ‘standard’ mode significantly more often than in the ‘sideways’ mode to males, with the opposite pattern prevailing to other females.