sRNA acts as an adaptor in the transfer of amino acids into protein [1-5]. Since an organism may contain more than one variety of sRNA for a given amino acid, different coding specificities of the various adaptors would provide a mechanism for degeneracy in the code. In E. coli sRNA, several leucine-acceptors have been shown to respond differently to various synthetic polynucleotides [5,6]. The experiments reported here were undertaken to determine whether the separate leucyl sRNA's actually contribute leucine to different sites in natural polypeptide chains. Evidence that they do is presented in this paper.

fects changes the absorbance: (1) Unstacking the nucleotide pairs increases absorbance by ap- proximately 45 per cent at 250-280 mjs.(2) The difference spectrum for reaction of a T2-mimetic mixture of adenine, guanine, and cytosine with CH20 has its isosbestic points near 255 mA and maximum at 275 m/A.'4We estimate that the combined effects of denaturation and formylation lead to fractional absorbance increases, r, of 0.45, 0.49, and 0.54 at 255, 258, and 260 m/s respec- tively.The absorbance that ordered C-RNA contributes to the solution (Ah) is therefore a/lr.fh is calculated from Ah and Ao, the absorbance before CH20 addition, as fh = (1 + r)Ah/(AO + Ah) = (1 + r)aA/r(Ao + a").For sample 11, the values of fh calculated in this way at 255, 258, and 260 mu are 0.57, 0.59, and.0.55 respectively.Averaged values of Ah are listed in Table 1.They are consistently lower than fh calculated from the thermal transition data (e.g., Fig. 1).

If two or more nucleotide sequences specify the same amino acid, the code is said to be degenerate for that amino acid. Evidence that such degeneracy exists in E. coli comes from experiments on the stimulation of ribosomal incorporation of amino acids by synthetic polyribonucleotides. For instance, Martin et al. [1] and Speyer et al. [2] found that either poly UC or poly UG stimulates incorporation of leucine, so that at least two different combinations code for the same amino acid. Since the specificity of coding seems to reside in sRNA molecules functioning as adaptors [3,4], such degeneracy might be due to the existence of two sRNA acceptors for leucine, each having different coding properties. Two peaks of leucine-acceptor activity were demonstrated in yeast sRNA by Doctor et al. [5] using countercurrent distribution. Berg and Lagerkvist [6] have shown that E. coli sRNA also contains two leucine acceptors with different acceptor-terminal nucleotide sequences. In this paper, two leucine acceptors in E. coli, separated by countercurrent distribution, are shown to have different coding properties. One responds preferentially to poly UC, the other to poly UG.

We introduce an intuitive particle-based model of time-symmetric quantum physics that gives a concrete description of what goes on in the time between projective measurements of a quantum system. The time-symmetry in this model means that we ...Physical interpretations of the time-symmetric formulation of quantum mechanics, due to Aharonov, Bergmann, and Lebowitz are discussed in terms of weak values. The most direct, yet somewhat naive, interpretation uses the time-symmetric formulation to ...

With advancements in stem cell technology, in vitro models using iPSC (induced pluripotent stem cells)-derived cardiomyocytes (iPSC-CM) and engineered heart tissues (EHT) can serve as powerful tools for disease modeling and drug screening. ...Fluorescent reporters of cardiac electrophysiology provide valuable information on heart cell and tissue function. However, motion artifacts caused by cardiac muscle contraction interfere with accurate measurement of fluorescence signals. Although drugs ...

In an earlier paper,' a detailed examination was made of the structure of a small portion of the genetic map of phage T4, the rIl region.This region, which controls the ability of the phage to grow in Escherichia coli strain K, consists of two adjacent cistrons, or functional units.Various rII mutants, unable to grow in strain K, have mutations affecting various parts of either or both of these cistrons.The topology of the region; i.e., the manner in which its parts are interconnected, was intensively tested and it was found that the active structure can be described as a string of subelements, a mutation constituting an alteration of a point or segment of the linear array.This paper is a sequel in which inquiry is made into the topography of the struc- ture, i.e., local differences in the properties of its parts.Specifically, are all the subelements equally mutable?If so, mutations should occur at random throughout the structure and the topography would be trivial.On the other hand, sites or regions of unusually high or low mutability would be interesting topographic fea- tures.The preceding investigation of topology was done by choosing mutants showing no detectable tendency to revert.This avoided any possible confusion between recombination and reverse mutation, so that a qualitative (yes-or-no) test for re-

One of the steps in protein biosynthesis appears to be the attachment of each amino acid to a specific acceptor (SRNA) molecule. According to the adaptor hypothesis, each SRNA molecule would then fit to a specific complementary base sequence on a linear RNA template, specifying the sequence of amino acids in the resultant protein [1,2]. An adaptor molecule thus could have two specificities: one recognizing the correct amino acid and activating enzyme; the other, the proper position on the template. The correctness of the amino-acid sequence therefore would depend upon the precision and constancy of the adaptors. However, the structures of the enzymes and adaptors are presumably under the genetic control of the organism and might be subject to heritable modifications. It is therefore conceivable that one or both ends of an adaptor might change sufficiently to cause occasional errors and, in the long run, an alteration of the genetic code might evolve. This notion, prompted by genetic observations [3] which suggested that mutation of a bacterium might modify its translation of genetic information, lead to the present comparison of the specificities of the acceptor RNA and activating enzymes of different organisms. Several differences in specificity have been reported previously. Berg et al. [4] demonstrated that SRNA from Escherichia coli contains two distinguishable acceptors for methionine. An enzyme prepared from yeast could attach methionine to one of these, while the enzyme from E. coli could attach to both. Webster found, in pig liver, a difference between the nuclear and cytoplasmic attachment enzymes for alanine. Rendi and Ochoa [6] noted that, for leucine, the enzymes in yeast and in E. coli could attach only to their homologous SRNA. Furthermore, in the case of leucine, rat liver enzyme and SRNA were interchangeable with those from E. coli. The observations presented below show that whether the enzymes and/or acceptors from two organisms are interchangeable depends upon not only the organisms in question but also the particular amino acid

A procedure is described for the efficient disjoining of the even-numbered T bacteriophages into structural components. Tail fibres and tail sheaths from T2L have been separated and purified, and sheaths can be obtained from the other T-even phages. The components have been characterized by electron microscopy using the phosphotungstate method and by chemical and physical methods. The tail of the bacteriophage consists of a sheath surrounding a core at the base of which are attached tail fibres. The sheath appears to be built of helically arranged subunits which form a hollow cylinder. We have confirmed that the sheath can contract in length, and have shown that the contraction is accompanied by an increase in diameter such that the volume of the sheath is approximately conserved. The core of the tail has been found to be a hollow cylinder with the central hole 25 Å in diameter. Chemical studies, using fingerprinting, suggest that the sheath is composed of about 200 repeated subunits of approximately 50,000 molecular weight. No N-terminal amino acid could be detected in sheaths. Fingerprints confirm the previous finding that the head membrane of the phage is composed of a large number of repeated subunits with a molecular weight of 80,000. The tail fibres appear to have a subunit with a molecular weight not less than 100,000. These studies show that the proteins composing the head, sheath and tail fibres of the phage have different primary structures.

The present research uncovers the dynamic nature of student discipline. The findings show that discipline escalates during the school year, that discipline escalates more severely for Black students, and that racial disparities in discipline ...Researchers have long used end-of-year discipline rates to identify punitive schools, explore sources of inequitable treatment, and evaluate interventions designed to stem both discipline and racial disparities in discipline. Yet, this approach leaves us ...

BENZERbarrier.One would thus achieve a substance which could be administered in an unobjectionable way (peripherally) and which would be expected to control the mental aberration.After this work had been completed, a paper appeared" describing effects of LSD- 25 on Siamese fighting fish.It was interesting to note that LSD-25 caused these animals to swim backward especially by action of the pectoral fins. SUMMARYThe administration of lysergic acid diethylamide (LSD-25) to mice caused them to behave in a way similar to untreated mice faced with the prospect of sliding down an inclined plane.It was believed that the drug induced in the mice an hallu- cination of sliding down an inclined plane.This abnormal behavior was pre- vented in some of the animals by injection of serotonin plus carbamylcholine into the lateral ventricle of the brain.The carbamylcholine could be replaced by the cholinesterase inhibitor physostigmine.The serotonin plus carbamylcholine had to be given intracerebrally.Intraperitoneal injection was ineffectual.Even by the intracerebral route, however, it was not possible to counteract LSD-25 in all the animals.Detailed data showing the antagonism between serotonin and LSD-25 in isolated segments of carotid arteries were recorded.The behavioral change caused in mice by LSD-25 was viewed as resulting from a cerebral deficiency of serotonin induced by this antimetabolite.

Phage-bacterium complexes of phages T2 and T7 on Escherichia coli B were inactivated by UV, photoreactivated, and then subjected to a second UV irradiation. Photoreactivated complexes had the same sensitivity to UV as reactivated complexes at the same survival level. This result is in agreement with the hypothesis that photoreactivation is effected by a direct reversal of the primary UV damage, rather than by a by-pass mechanism which circumvents the effect of the damage.

Bacteriophage is utilized as a discriminating device for determining the distribution of an inducible enzyme (β-D-galactosidase) in the cells of a culture of bacteria (E. coli B). It is shown that the cellular distribution of enzyme is given by the shape of the curve of enzyme released vs number of cells lysed.

minutes. In the case of T7, however, the small change in slope may well be due to a screening effect.

Rectifying current-voltage characteristics going up to several hundred volts inverse have been observed in metal-germanium point contact rectifiers. A reproducible negative differential resistance region occurs in the inverse characteristic. Certain impurities are desirable in producing high voltage material. Surface treatment, e.g., by etching, is very important. The metal used as a whisker has little effect. Increasing the force of contact increases greatly the current of low voltages but has less effect on the high voltage curve. Pronounced improvement of rectification can be effected by treatment of the contact with large currents. Variation with temperature is very marked, especially for crystals of large inverse resistance; the variation of the inverse peak with temperature indicates that contact heating is responsible for the negative resistance. Time lags in the inverse negative resistance region of the order of 10−5 second occur. When contact is made between two Ge crystals, typical inverse characteristics are observed in both directions. Photoelectric effects are observed and indicate that the barrier thickness is greater the higher the inverse peak voltage.