The Amphioxus Hox Cluster: Characterization, Comparative Genomics, and Evolution

The amphioxus Hox cluster is often viewed as “archetypal” for the chordate lineage. Here we present a descriptive account of the 448kb region spanning the Hox cluster of the amphioxus Branchiostoma floridae from Hox14 to Hox1.We provide complete coding sequences of all 14 previously described amphioxus sequences and describe a detailed analysis of the conserved non-coding regulatory sequence elements. We find that the posterior part of the Hox cluster is so highly derived that even the complete genomic sequence is insufficient to decide whether the posterior Hox genes arose by independent duplications or whether they are true orthologs of the corresponding gnathostome paralog groups. In contrast, the anterior region is much better conserved. The amphioxus Hox cluster strongly excludes repetitive elements with the exception of two repeat islands in the posterior region. Repeat exclusion is also observed in gnathostomes, but not protostome Hox clusters. We thus hypothesize that the much shorter vertebrate Hox clusters are the result of extensive resolution of the redundancy of regulatory DNA following the genome duplications rather than the consequence of a selection pressure to remove non-functional sequence from the cluster

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

High-Resistance Resistor Consisting of a Subthreshold CMOS Differential Pair

We propose a CMOS circuit that can be used as an equivalent to resistors. This circuit uses a simple differential pair with diode-connected MOSFETs and operates as a high-resistance resistor when driven in the subthreshold region of MOSFETs. Its resistance can be controlled in a range of 1-1000 M Omega by adjusting a tail current for the differential pair. The results of device fabrication with a 0.35-mu m 2P-4M CMOS process technology is described. The resistance was 13 M Omega for a tail current of 10 nA and 135 M Omega for 1 nA. The chip area was 105 mu m x 110 mu m. Our resistor circuit is useful to construct many high-resistance resistors in a small chip area

Low-Voltage Process-Compensated VCO with On-Chip Process Monitoring and Body-Biasing Circuit Techniques

A voltage-controlled oscillator (VCO) tolerant to process variations at lower supply voltage was proposed. The circuit consists of an on-chip threshold-voltage-monitoring circuit, a current-source circuit, a body-biasing control circuit, and the delay cells of the VCO. Because variations in low-voltage VCO frequency are mainly determined by that of the current in delay cells. a current-compensation technique was adopted by using an on-chip threshold-voltage-monitoring circuit and body-biasing circuit techniques. Monte Carlo SPICE simulations demonstrated that variations in the oscillation frequency by using the proposed techniques were able to be suppressed about 65% at a I-V supply voltage, compared to frequencies with and without the techniques

A1-μW 600-ppm/℃ Current Reference Circuit Consisting of Subthreshold CMOS Circuits

A low-power CMOS current reference circuit was developed using a 0.35-μm standard CMOS process technology. The circuit consists of MOSFET circuits operating in the subthreshold region and uses no resistors. It compensates for the temperature effect on mobility μ and threshold voltage V_[TH] of MOSFETs and generates a reference current that is insensitive to temperature and supply voltage. Theoretical analyses and experimental results showed that the circuit generates a stable reference current of 100 nA. The temperature coefficient of the current was 520 ppm/℃ at best and 600 ppm/℃ on average in the range of 0 ℃-80 ℃. The line regulation was 0.2%/V in a supply voltage range of 1.8-3 V. The power dissipation was 1μW, and the chip area was 0.015 mm2. Our circuit would be suitable for use in subthreshold-operated power-aware large-scale integrations

An On-Chip PVT Compensation Technique with Current Monitoring Circuit for Low-Voltage CMOS Digital LSIs

An on-chip process, supply voltage, and temperature (PVT) compensation technique for low-voltage CMOS digital circuits was proposed. Because the degradation of circuit performance originates from the variation of the saturation current in transistors, we developed a compensation circuit consisting of a reference current that is independent of PVT variations. The circuit is operated so that the saturation current in digital circuits is equal to the reference current. The operations of the circuit were confirmed by SPICE simulation with a set of 0.35-μm standard CMOS parameters. Monte Carlo simulations showed that the proposed technique effectively improves circuit performance by 71%. The circuit is useful for on-chip compensation to mitigate the degradation of circuit performance with PVT variation in low-voltage digital circuits