Mixed lipid films of dimyristoylphosphatidylcholine and its amide-containing analog, l,2-bis(myristoylamido)-l,2-deoxyphosphatidylcholine (DDPC) were investigated, both as mixed monolayers at the air-water interface and solvent-cast films on solid surfaces. Monolayer isotherms of these films at the air-water interface at various temperatures and at various compositions revealed diffuse first-order phase transitions for these systems and phase-mixed behavior, with the addition of more DDPC leading to more diffuse transitions and expanded films. Mixing diagrams show positive deviations from ideal mixing that disappear at higher lateral surface pressures, indicating stearic constraints limit mixing at lower surface pressures. Fluorescence microscopy of these films at the air-water interface shows coexistence behavior in the phase-transition region consistent with phase mixing. Fourier transform IR studies of solvent-cast films show evidence of hydrogen bonding between the two-component lipids strongly contributing to this phase behavior.

Regulation of replication origins is important for complete duplication of the genome, but the effect of origin activation on the cellular response to replication stress is poorly understood. The budding yeast ribosomal RNA gene (rDNA) forms tandem repeats and undergoes replication fork arrest at the replication fork barrier (RFB), inducing DNA double-strand breaks (DSBs) and genome instability accompanied by copy number alterations. Here we demonstrate that the S-phase cyclin Clb5 promotes rDNA stability. Absence of Clb5 led to reduced efficiency of replication initiation in rDNA but had little effect on the amount of replication forks arrested at the RFB, suggesting that arrival of the converging fork is delayed and forks are more stably arrested at the RFB. Deletion of CLB5 affected neither DSB formation nor its repair at the RFB, but led to homologous recombination-dependent rDNA instability. Therefore, arrested forks at the RFB may be subject to DSB-independent, recombination-dependent rDNA instability. The rDNA instability in clb5Δ was not completely suppressed by the absence of Fob1, which is responsible for fork arrest at the RFB. Thus, Clb5 establishes the proper interval for active replication origins and shortens the travel distance for DNA polymerases, which may reduce Fob1-independent DNA damage.

Common ancestors of vertebrates had four types of cone opsins: short-wavelength sensitive 1 (SWS1), SWS2, rhodopsin 2 (RH2), and long-wavelength sensitive (LWS) types. Whereas fish and birds retain all the types, mammals have lost two of them (SWS2 and RH2) possibly because of their nocturnal lifestyle during the Mesozoic Era. Considering that the loss of cone opsin types causes so-called color blindness in humans (e.g., protanopia), the ability to discriminate color by trichromatic humans could be lower than that in potentially tetrachromatic birds and fish. Behavioral studies using color-blind (cone opsin-knockout) animals would be helpful to address such questions, but it is only recently that the genome-editing technologies have opened up this pathway. Using medaka as a model, we introduced frameshift mutations in SWS2 (SWS2a and/or SWS2b) after detailed characterization of the loci in silico, which unveiled the existence of a GC-AG intron and non-optic expressed-sequence-tags (ESTs) that include SWS2a in part. Transcripts from the mutated SWS2 loci are commonly reduced, suggesting that the SWS2a/b-double mutants could produce, if any, severely truncated (likely dysfunctional) SWS2s in small amounts. The mutants exhibited weakened body color preferences during mate choice. However, the optomotor response (OMR) test under monochromatic light revealed that the mutants had no defect in spectral sensitivity, even at the absorbance maxima (λ max) of SWS2s. Evolutionary diversification of cone opsins has often been discussed in relation to adaptation to dominating light in habitats (i.e., changes in the repertoire or λ max are for increasing sensitivity to the dominating light). However, the present results seem to provide empirical evidence showing that acquiring or losing a type of cone opsin (or changes in λ max) need not

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