Patterning of heteroepitaxial overlayers from nano to micron scales.

Thin heteroepitaxial overlayers have been proposed as templates to generate stable, self-organized nanostructures at large length scales, with a variety of important technological applications. However, modeling strain-driven self-organization is a formidable challenge due to different length scales involved. In this Letter, we present a method for predicting the patterning of ultrathin films on micron length scales with atomic resolution. We make quantitative predictions for the type of superstructures (stripes, honeycomb, triangular) and length scale of pattern formation of two metal-metal systems, Cu on Ru(0001) and Cu on Pd(111). Our findings are in excellent agreement with previous experiments and call for future experimental investigations of such systems.

Codon-specific serine transfer ribonucleic acid synthesis in avian liver during vitellogenin induction.

The relative rates of synthesis of two major tRNASer species in rooster liver were simultaneously assessed during induction by estradiol-17beta of the synthesis of a serine-rich phosphoprotein, vitellogenin. The relative rates of tRNA synthesis were determined by a double-label method in which nonspecific effects of the hormone were avoided. Isotope ratios of highly purified tRNASer species were measured following an in vivo labeling procedure which included a 7-day labeling period with [5-3H]orotic acid prior to, and a 6 h labeling with [6-14C]orotic acid from 42 h after the hormone injection. tRNASer (AGU,C) and tRNASer (UCU,C,A) were extensively purified by chromatography on benzoylated DEAE-cellulose in the presence and absence of Mg2+. In three separate labeling experiments the rate of tRNASer (UCU,C,A) synthesis was slightly but not significantly increased relative to the rate of tRNASer (AGU,C) synthesis during the period when vitellogenin was synthesized at a constant rate and the level of tRNASer continued to rise. The results suggest that mechanisms other than a differential rate of transcription are involved in the regulation of tRNASer levels in avian liver during vitellogenin induction.

Codon-specific serine transfer ribonucleic acid degradation in avian liver during vitellogenin induction.

The relative rates of degradation of two major tRNASer species in rooster liver were simultaneously assessed during induction by estradiol-17 beta benzoate of the synthesis of a serine-rich phosphoprotein, vitellogenin. The relative rate of degradation was determined by an in vivo pulse-chase labeling method, which included a 24-h labeling period with [5-3H]orotic acid prior to and a 6-day chase period with nonradioactive orotic acid after the administration of estrogen. tRNA Ser(AGU,C) and tRNASer (UCU,C,A) were extensively purified by chromatography on benzoylated DEAE-cellulose in the presence and absence of Mg2+ and their radioactivities determined. In three separate labeling experiments, the difference in radioactivity of pulse-labeled and chased tRNASer (AGU,C) vs. that of tRNASer(UCU,C,A) was approximately 2-fold, suggesting a slower rate of degradation of tRNASer(AGU,C) during vitellogenin induction. Calculation of the approximate half-lives of the two tRNASer species indicates that the half-life of tRNASer (AGU,C) was increased from 3.1 days to 6.2 days during vitellogenin induction, while that of tRNASer (UCU,C,A) was essentially unchanged (2.6 days). Regulation of tRNA degradation which is possibly connected with the frequency of its use in ribosomal protein synthesis may help to explain why, in many differentiated cells, the tRNA population is adapted to the amino acid composition of the synthesized proteins.