Transport properties of rigid, symmetrical oligomeric structures composed of prolate, ellipsoidal subunits

We have calculated translational and rotational diffusion coefficients and intrinsic viscosities of oligomeric structures composed of n identical subunits having a prolate ellipsoidal shape with axial ratio p. Results are presented for p = 1-6 for a variety of structures with n = 1-6. We compare our results with those obtained by a different modeling procedure, proposed by other workers, in which the monomeric subunit is represented as a string of touching, colinear spheres. If n and an estimate of p are known, the structure of the oligomer can be. in most cases, unambiguously determined by comparison of the experimental oligomer-to-monomer ratios of a given property with the numerical results of this work. As examples of the applicability of our results, we examine the relationship between structure and properties for neurophysin. bovine serum albumin, hemoglobin and phycocyanin.     

An efficient method for finding repeats in molecular sequences.

The problem of finding repeats in molecular sequences is approached as a sorting problem. It leads to a method which is linear in space complexity and NlogN in expected time complexity. The implementation is straightforward and can therefore be used to handle large sequences with relative ease. Of particular interest is that several sequences can be treated as a single sequence. This leads to an efficient method for finding dyads and for finding common features of many sequences, such as favorable alignments.     

Methylation of the Flagellin of Salmonella typhimurium

The methylation of endogenous proteins by Salmonella typhimurium SL 870 was investigated in cell-free extracts by using S-adenosylmethionine as methyl donor. Several lines of evidence are presented which suggest that one of the methylated products is the protein flagellin. Mutant strains of SL 870 (nml⁻fla⁺ and nml⁺fla⁻) were also found to synthesize epsilon-N-methyl-lysine. It is proposed that S. typhimurium possesses at least two genes specifying different methylating enzymes. One gene product is a flagellin-specific methylating enzyme, whereas the other gene(s) codes for enzymes that methylate one or more other cell proteins.     

Nuclear Magnetic Resonance Studies of Sodium Ions in Isolated Frog Muscle and Liver

Nuclear magnetic resonance (NMR) was used to determine Na⁺ complexing in muscle and liver (at 23°C) from bullfrogs (Rana catesbeiana) and to study the influence of temperature on Na⁺ complexing in muscle from leopard frogs (Rana pipiens). The Na⁺ complexed in muscle and liver was found to be 36.6 ± 4.6% and 66.1 ± 3.5% respectively. A temperature decrease from +34°C to -2°C results in a 20% decrease in the mobility of the free Na⁺ in the fresh muscle. This 20% decrease in mobility results in about 50% of the free Na⁺ at 34°C being complexed at the lower temperature.     

Phytochrome in etiolated annual rye

Summary During a seven-fold increase in length the content of the coleoptile in photoreversible phytochrome increased four-fold and that of the primary leaf nine-fold. The phytochrome content, during growth, expressed on a fresh- or dry-weight basis did not vary greatly for either organ. Phytochrome per mg dry weight (OD⁷³⁰/mg=0.5) was nearly the same in the leaf as in the coleoptile. Coleoptiles studied had a constant DNA content of 4.1 g per organ. DNA content of the leaf increased with age. Phytochrome per DNA was much higher in the coleoptile than in the primary leaf and increased with growth in each of these organs. Thus, there was not a constant amount of phytochrome per cell in either tissue with increasing age and there was not the same amount of phytochrome per cell in the coleoptile as in the primary leaf at any age.This work was supported in part by U.S. Atomic Energy Commission Contract No. AT (30-I)2373.     

On the derivation of a mean growth equation for cell cultures

IfN(t) is the expected number of cells in a culture at timet, the corresponding time derivative, andf(t−τ)dt the probability that a cell of aget−τ at timet will divide in the succeeding time intervaldt, then according to Hirsch and Engelberg (this issue) there obtains the integral equation for describing the dynamics of the cell population. It is the purpose of this note to give two alternative derivations of this equation, one based on the age density equation of Von Foerster, and the other based on a generalized form of the Harris-Bellman equation describing the first moment of an age dependent, branching process. In addition, a probability model is posed from which the Von Foerster equation and, hence, the Hirsch-Engelberg equation readily follows.     

IL-4 inhibits IL-2 receptor expression and IL-2-dependent proliferation of human T cells

Recent studies have shown that IL-4 can affect lymphocyte responses to IL-2. To evaluate the effects of IL-4 on T cell responses to physiologically relevant stimuli, we studied normal human T cells cultured with a low concentration of anti-CD3 mAb and IL-2 in the presence and absence of added IL-4. The addition of IL-4 to cultures of T cells stimulated with anti-CD3 mAb and IL-2 reduced the proliferative response by 49 to 59%. The inhibitory effect was observed in 3-, 5-, and 7-day cultures. Inhibition was dose-dependent with maximal inhibition at concentrations greater than or equal to 5 to 10 U/ml IL-4. IL-4-mediated inhibition occurred early during the T cell response, inasmuch as addition of IL-4 after stimulation for 24 h did not result in significant inhibition. Phenotypic analyses of cells cultured in the presence of anti-CD3 mAb, IL-2, and IL-4 suggested that the mechanism of regulation by IL-4 involves the inhibition of IL-2R expression. The proportion of both CD4+ and CD8+ cells that expressed IL-2R in response to IL-2 was diminished in the presence of IL-4, although HLA-DR levels were unaffected. Soluble IL-2R was also reduced in supernatants of cultures stimulated with anti-CD3 mAb, IL-2, and IL-4 as compared to cultures stimulated with anti-CD3 mAb and IL-2. These findings indicate that when normal human T cells are stimulated in vitro in a manner that approximates a physiologic interaction with Ag in vivo, rIL-4 provides a potent inhibitory signal to IL-2 responsive cells that is likely mediated by IL-4-induced inhibition of IL-2R expression.