Expression of the tryptophan (trp) operon of Escherichia coli was shown to be regulated by attenuation in an in vitro DNA-dependent protein-synthesizing system. In extracts prepared from a temperature-sensitive tryptophanyl-tRNA synthetase mutant, plasmid-directed trpE enzyme synthesis was inhibited 2- to 3-fold by addition of purified wild type tryptophanyl-tRNA synthetase. When the extract us...

It is shown that a surface wave will be generated by a horizontal.slot situated above a corrugated or dielectric-coated guiding surface. A physical interpretation of the analysis is suggested which explains the mechanism of launching in terms of a resonance phenomenon allied to that which arises when a piston attenuator is terminated by a reactance equal and opposite to its own (reactive) chara...

We fabricate and measure a microfluidic variable optical attenuator, which consists of an optical waveguide integrated with a microfluidic channel. An opening is introduced in the upper cladding of the waveguide in order to facilitate the alignment and bonding of the microfluidic channel. By using fluids with different refractive indices, the optical output power is gradually attenuated. We obt...

into the effective operation of variable gain amplifiers (VGA) in automatic gain control (AGC) applications. Figure 1 is a general block diagram for an AGC loop. The input signal passes through the VGA to produce the output level to be stabilized. The detector’s output is compared against a setpoint voltage to produce an error signal, which is then integrated to produce a gain control voltage. ...

We have isolated two regulatory mutants altered in the leader region of the Escherichia coli tryptophan (trp) operon. In one mutant, trpL29, the AUG translation start codon for the trip leader peptide is replaced by AUA. The other mutant, trpL75, has a G leads to A change at residue 75, immediately after the UGA translation stop codon for the trp leader peptide. In vivo, trpL29 and trpL75 incre...

In HIV-1 infection, Tat acts at least in part to control transcriptional elongation by overcoming premature transcriptional termination. In some other genes this process is governed by DNA elements called attenuators in concert with cellular transcription factors. To understand the action of Tat more fully and explore its role as an anti-attenuator, we examined the ability of several natural an...

Mutants of the histidine operon control region (hisO) include two classes: (1) those completely unable to express the operon (His auxotrophs), and (2) prototrophs that are unable to achieve fully induced levels of operon expression (still His+ but sensitive to the drug amino-triazole). Using new, as well as previously existing hisO mutants, we constructed a fine-structure deletion map of GO. Mu...