Molecular cloning and chromosomal mapping of type one serine/threonine protein phosphatases in Arabidopsis thaliana

Type one serine/threonine protein phosphatases (PP1s) have been implicated in various processes of plant growth and development. In all plant species studied, PP1s are encoded by multigene families. Previous studies in our laboratory identified five Arabidopsis thaliana PP1 genes (TOPP1, TOPP2, TOPP3, TOPP4 and TOPP5). In the present study, we report the isolation of three additional PP1 genes (TOPP6, TOPP7 and TOPP8). Southern blot analyses indicate that these three newly isolated genes are single-copy genes in A. thaliana genome. All the three genes are expressed in roots, rosettes and flowers, although their expression levels appear to be lower than those of the five previously identified TOPP genes. Six of the eight TOPP genes were mapped to different positions on four of five A. thaliana chromosomes. Sequence comparison revealed that TOPP genes belong to different subgroups of plant PP1 genes, suggesting that they may encode proteins with distinct functions.     

Autoregulation of the nar operon encoding nitrate reductase in Escherichia coli

Summary Nitrate reductase is demonstrated to exert an autogenous control on its own synthesis. This effect requires the participation of the molybdenum cofactor. Use of strains in which the control region of the nar operon is mutated reveals two loci in this region: one, affected in strain LCB94, is common to both autoregulation and induction by nitrate while the other, mutated in strain LCB188, is specific for the induction by nitrate. It is proposed that the autogenous control prevents the unnecessary accumulation of the nitrate reductase subunits in the cytoplasm.     

Hypothesis: spring-loaded boomerang mechanism of influenza hemagglutinin-mediated membrane fusion

Substantial progress has been made in recent years to augment the current understanding of structures and interactions that promote viral membrane fusion. This progress is reviewed with a particular emphasis on recently determined structures of viral fusion domains and their interactions with lipid membranes. The results from the different structural and thermodynamic experimental approaches are synthesized into a new proposed mechanism, termed the “spring-loaded boomerang” mechanism of membrane fusion, which is presented here as a hypothesis.     

JNK signaling is needed to tolerate chromosomal instability

Chromosomal instability (CIN), as a common feature of tumors, represents a potential therapeutic target if ways can be found to specifically cause apoptosis in unstably dividing cells. We have previously shown that if signaling through the JNK pathway is reduced, apoptosis is triggered in models of chromosomal instability induced by loss of the spindle checkpoint. Here we identify components upstream and downstream of JNK that are able to mediate this effect, and test the involvement of p53 and DNA damage in causing apoptosis when JNK signaling is reduced in CIN cells. We show that cell cycle progression timing has a strong effect on the apoptosis seen when JNK signaling is reduced in genetically unstable cells: a shortened G₂ phase enhances the apoptosis, while lengthening G₂ rescues the JNK-deficient CIN cell death phenotype. Our findings suggest that chromosomal instability represents a significant stress to dividing cells, and that without JNK signaling, cells undergo apoptosis because they lack a timely and effective response to DNA damage.     

Structure of a New Nor-kaurenolide from Gibberella fujikuroi

A novel metabolite from Gibberella fujikuroi was isolated and its structure was elucidated as 4β,7β-dihydroxy-18-norkaurenolide (I).