Antagonism between growth and flocculation inPichia stipitis NRRL Y-7124:Influence of Ca +2 and Mg +2 ions

Summary The effects of Mg⁺² and Ca⁺² ion concentrations onPichia stipitis growth and flocculation were studied by a 2×2 factorial design. Negative interaction was detected between these ions (p<0.01): maximum growth rate was attained with high Mg⁺² (3 mM) and low Ca⁺² (0.34 mM) concentration levels, whereas the inverse ionic ratio was required to reach the maximum flocculation extent. Neither stimulatory or inhibitory effects on growth or flocculation were observed by increasing other cations (Zn⁺², Mn⁺², Co⁺², Fe⁺²) or vitamins concentration. An antagonistic relationship between growth and flocculation was concluded.     

The evolution and socioecology of dominance in primate groups: A theoretical formulation,classification and assessment

Dominance hierarchies are presumed to evolve by individual selection from an evolutionary compromise between intraspecific competition for resources and for mates. The hypothesis is put forward that when competition in “stable” habitats leads to “niche breadth,” a species is preadapted to life in heterogeneous environments and the consequent selection for fecundity. Status patterns are viewed as systems of signals communicating differential tendencies among individuals to attack or retreat, and a simple graphical model is presented which relates the costs or benefits to fitness of aggressive or appeasement behavior and interindividual distance. Primate societies are classified on the basis of their dominance hierarchies, and the ecological correlates of these patterns are discussed. Based on hypotheses presented in the paper, topics for future research are suggested.     

Asymmetric maturation of a dimeric transfer RNA precursor

Six of the eight transfer RNAs coded by bacteriophage T4 are synthesized via three dimeric precursor molecules. The sequences of two of these have been determined. Both of these precursors give rise to equimolar amounts of the cognate tRNA molecules in vivo. In contrast, even in wild-type infections, tRNA^Ile is present in ≤ 30% the amount of tRNA^Thr, with which it is processed from a common dimeric precursor.We have now determined the sequence of this dimer. In addition to the nucleotides present in tRNA^Thr and tRNA^Ile, it contains nine precursor-specific residues, located at the 5′ and 3′ termini and at the interstitial junction of the two tRNA sequences. While the three dimers share the majority of structural features in common, pre-tRNA^{Thr + Ile} is the only case in which an encoded tRNA 3′ -C-C-A terminus is present in the interstitial region.The processing of this dimer in various biosynthetic mutants has been analyzed in vivo and in vitro and shown to be anomalous in several respects. These results suggest that the apparent underproduction of tRNA^Ile can be explained by a novel processing pathway that generates a metabolically unstable tRNA^Ile product. Data from DNA sequence analysis of the T4 tRNA gene cluster (Fukada & Abelson, 1980) support the conclusion that the asymmetric maturation of this precursor is a consequence of the unique disposition of the -C-C-A sequence. These results argue that gene expression can be modulated at the level of RNA processing. The biological significance of this phenomenon is discussed in relation to evidence that tRNA^Ile has a unique physiological role.     

Three RNA recognition motifs participate in RNA recognition and structural organization by the pro-apoptotic factor TIA-1

T-cell intracellular antigen-1 (TIA-1) regulates developmental and stress-responsive pathways through distinct activities at the levels of alternative pre-mRNA splicing and mRNA translation. The TIA-1 polypeptide contains three RNA recognition motifs (RRMs). The central RRM2 and C-terminal RRM3 associate with cellular mRNAs. The N-terminal RRM1 enhances interactions of a C-terminal Q-rich domain of TIA-1 with the U1-C splicing factor, despite linear separation of the domains in the TIA-1 sequence. Given the expanded functional repertoire of the RRM family, it was unknown whether TIA-1 RRM1 contributes to RNA binding as well as documented protein interactions. To address this question, we used isothermal titration calorimetry and small-angle X-ray scattering to dissect the roles of the TIA-1 RRMs in RNA recognition. Notably, the fas RNA exhibited two binding sites with indistinguishable affinities for TIA-1. Analyses of TIA-1 variants established that RRM1 was dispensable for binding AU-rich fas sites, yet all three RRMs were required to bind a polyU RNA with high affinity. Small-angle X-ray scattering analyses demonstrated a "V" shape for a TIA-1 construct comprising the three RRMs and revealed that its dimensions became more compact in the RNA-bound state. The sequence-selective involvement of TIA-1 RRM1 in RNA recognition suggests a possible role for RNA sequences in regulating the distinct functions of TIA-1. Further implications for U1-C recruitment by the adjacent TIA-1 binding sites of the fas pre-mRNA and the bent TIA-1 shape, which organizes the N- and C-termini on the same side of the protein, are discussed.