Viscosity-Induced Emission of 5-(Diarylmethylene)imidazolone with Extended Conjugation via Attachment of N-Methylpyrrole at the 2-Position.

We have developed a series of 2-monoaryl-5-diarylmethylene analogs of the green fluorescent protein chromophore to study their viscosity-induced emission (VIE) properties. The analogs were synthesized by a condensation with methyl imidate and N-(diarylmethylene)glycinate. Among the analogs, the N-methylpyrrol-2-yl-substituted analog 1h induced the most remarkable VIE behavior in triglyceride and lipid bilayers probably due to the high π-electron-rich property of the pyrrole ring. The pyrrole substituent in imidazolone analogs can be expected to become a common template for introducing VIE behavior.

Initiation of DNA replication after fertilization is regulated by p90Rsk at pre-RC/pre-IC transition in starfish eggs.

Initiation of DNA replication in eukaryotic cells is controlled through an ordered assembly of protein complexes at replication origins. The molecules involved in this process are well conserved but diversely regulated. Typically, initiation of DNA replication is regulated in response to developmental events in multicellular organisms. Here, we elucidate the regulation of the first S phase of the embryonic cell cycle after fertilization. Unless fertilization occurs, the Mos-MAPK-p90Rsk pathway causes the G1-phase arrest after completion of meiosis in starfish eggs. Fertilization shuts down this pathway, leading to the first S phase with no requirement of new protein synthesis. However, how and in which stage the initiation complex for DNA replication is arrested by p90Rsk remains unclear. We find that in G1-arrested eggs, chromatin is loaded with the Mcm complex to form the prereplicative complex (pre-RC). Inactivation of p90Rsk is necessary and sufficient for further loading of Cdc45 onto chromatin to form the preinitiation complex (pre-IC) and the subsequent initiation of DNA replication. However, cyclin A-, B-, and E-Cdk's activity and Cdc7 accumulation are dispensable for these processes. These observations define the stage of G1 arrest in unfertilized eggs at transition point from pre-RC to pre-IC, and reveal a unique role of p90Rsk for a negative regulator of this transition. Thus, initiation of DNA replication in the meiosis-to-mitosis transition is regulated at the pre-RC stage as like in the G1 checkpoint, but in a manner different from the checkpoint.

The N- and C-terminal mutations in tryptophan permease Tat2 confer cell growth in Saccharomyces cerevisiae under high-pressure and low-temperature conditions.

Tryptophan uptake appears to be the limiting factor in growth of tryptophan auxotrophic Saccharomyces cerevisiae strains under the conditions of high hydrostatic pressure and low temperature. When the cells are subjected to a pressure of 25 MPa, tryptophan permease Tat2 is degraded in a manner dependent on ubiquitination by Rsp5. One of the high-pressure growth-conferring genes, HPG2, was shown to be allelic to TAT2. The HPG2-1 (Tat2(E27F)) mutation site is located within the ExKS motif in the N-terminus, and the HPG2-2 (Tat2(D563N)) and HPG2-3 (Tat2(E570K)) mutation sites are located at the KQEIAE sequence in the C-terminus. The HPG2 mutations enhance the stability of Tat2 during high-pressure or low-temperature incubation, leading to cell growth under these stressful conditions. These results suggest that the cytoplasmic tails are involved in Rsp5-mediated ubiquitination of Tat2 under high-pressure or low-temperature conditions.