Aminoacyl-tRNA synthetase families and their significance to the origin of the genetic code

A correlation of various aspects of the protein structures and substrate and mechanistic specificities of the aminoacyl-tRNA synthetases has led to the identification of at least one family of enzymes probably derived from a common ancestral synthetase. While strong correlations exist only in one part of the array of 64 codons comprising the Genetic Code, this itself may be interpreted as a meaningful pattern, most consistent with a development of the present code from earlier codes containing fewer amino acids and fewer available codons. Specifically, strong correlations in the enzymes whose cognate tRNAs respond to codons containing a central pyrimidine, including the enzyme family of Ile-, Phe-, Val-, Met-, and Leu-tRNA synthetases, suggests that these enzymes evolved last, and that, therefore, an earlier version of the Genetic Code was comprised solely of codons containing a central purine. It is suggested that further study of the historical interrelationships of these enzymes could lead to a fairly detailed picture of how the Genetic Code developed.     

Structural features of human leukocyte interferon A as determined by circular dichroism spectroscopy

The solution structure of human leukocyte (alpha) interferon-A (LeIF-A) purified from E. coli extracts was investigated by circular dichroism spectroscopy. At pH 8.2, the native molecule exhibits 40-70% alpha-helix and no clearly detectable beta-structure. The tertiary structure includes a closely-packed interior containing at least one tryptophan side-chain. Titration to pH 1.5 produces a partial loss of structural features which are rapidly regained on return to neutral pH.     

Inclusion body formation by interleukin-1β depends on the thermal sensitivity of a folding intermediate

We show that sequence and growth temperature effects on IB formation in the small, monomeric β-barrel protein interleukin-1β (IL-1β) can be quantitatively reproduced in an in vitro system in which IL-1β is refolded from denaturant at different temperatures. The results suggest that temperature and mutational effects on IB formation may be based on intrinsic properties of the protein sequence rather than interactions with chaperones or other cellular factors. We also report striking correlations of IB formation with mutation-dependent changes in residue hydrophobicity. The nature of these trends differs considerably with residue position, however, suggesting that they are mediated by particular local environments created by an ordered structure.     

Constant rate allocation in nymphal development in species of Hemiptera

Abstract. This study investigated the existence of rate isomorphy (the constant allocation of relative times to different stages of development under different abiotic conditions) in Macrolophus pygmaeus (Hemiptera: Miridae; a phytophagous and predatory insect). Replicated data were used from a range of temperatures regarding (i) the developmental period of each nymphal stage in relation to the total duration of nymph development, when feeding on three host plants either with different prey species or without prey, and (ii) its egg, total nymphal and preoviposition period, on two host plants, with different prey species. The proportion of time required for the development of each nymphal stage of M. pygmaeus is not different among the temperatures or the kind of food available. These proportions ranged among the different host plants, temperatures and prey presence/absence from 17.3–21.8% in the first, 14.5–18.8% in the second, 14.2–18.3% in the third, 16.5–21.0% in the fourth and from 25.4–30.6% in the fifth nymphal stage. Thus, temperature does not significantly affect the proportion of time spent in each nymphal stage and rate isomorphy exists in nymphal development. This phenomenon was also investigated using data from the literature, and it also occurs in several other Hemiptera species. Therefore, there appears to be a constant time allocation in the nymphal development of the higher taxonomic groups of insects. However, for M. pygmaeus, rate isomorphy does not hold when considering egg‐to‐egg development and the relative duration of times to egg hatch, total nymphal development and preoviposition period. The ecophysiological implications of this rate isomorphy phenomenon are discussed in relation to endocrinological mechanisms. Apart from its theoretical interest, the existence of rate isomorphy simplifies studies on the rate of development and the estimation of thermal constants of an insect, which are essential for the prediction of insect population dynamics. It is also proposed that the term ‘rate isomorphy’ does not strictly describe the phenomenon, and it is suggested that ‘constant rate allocation’ would be a more suitable term.     

Cloning, functional expression and characterization of a human olfactory receptor.

The human olfactory system can recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants begins with the binding of an odorant ligand to a specific receptor protein on the olfactory neuron cell surface. To address the problem of olfactory perception at a molecular level, we have cloned, functionally expressed and characterized the first human olfactory receptor (OR 17-40). Application of a mixture of hundred different odorants elicited a transient increase in intracellular calcium at HEK 293-cells which were transfected with a plasmid containing the receptor encoding DNA and a membrane import sequence. By subdividing the odorant mixture in smaller groups we could identify a single component which represented the only effective substance: helional. Testing some structurally closely related molecules we found only one other compound which also could activate the receptor: heliotropyl acetone. All other compounds tested were completely ineffective. These findings represent the beginning of molecular understanding of odorant recognition in humans.