RESUMEN
Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.
RESUMEN
Tyrosine phosphorylation of proteins in the yeast Saccharomyces cerevisiae has been examined following exposure to the mating pheromone alpha-factor. When a cells are treated with alpha-factor a protein of approximately 40 kDa molecular weight is tyrosine phosphorylated. This tyrosine phosphorylation response requires an intact signal transduction pathway, is not restricted to a short interval of the cell division cycle, and requires protein synthesis for its maximal accumulation. Mating competent fus3 deletion strains fail to elaborate the phosphotyrosine response. The possibility that FUS3 encodes the 40 kDa protein is discussed.
Asunto(s)
Proteínas Fúngicas/metabolismo , Péptidos/metabolismo , Saccharomyces cerevisiae/metabolismo , Tirosina/metabolismo , Western Blotting , Ciclo Celular , Cicloheximida/farmacología , Proteínas Fúngicas/antagonistas & inhibidores , Factor de Apareamiento , Peso Molecular , Fosforilación , Saccharomyces cerevisiae/citología , Saccharomyces cerevisiae/efectos de los fármacos , Transducción de SeñalRESUMEN
The DAT1 gene of Saccharomyces cerevisiae encodes a DNA binding protein (Dat1p) that specifically recognizes the minor groove of non-alternating oligo(A).oligo(T) tracts. Sequence-specific recognition requires arginine residues found within three perfectly repeated pentads (G-R-K-P-G) of the Dat1p DNA binding domain [Reardon, B. J., Winters, R. S., Gordon, D., and Winter, E. (1993) Proc. Natl. Acad. Sci. USA 90, 11327-1131]. This report describes a rapid and simple method for purifying the Dat1p DNA binding domain and the biochemical characterization of its interaction with oligo(A).oligo(T) tracts. Oligonucleotide binding experiments and the characterization of yeast genomic Dat1p binding sites show that Dat1p specifically binds to any 11 base sequence in which 10 bases conform to an oligo(A).oligo(T) tract. Binding studies of different sized Dat1p derivatives show that the Dat1p DNA binding domain can function as a monomer. Competition DNA binding assays using poly(I).poly(C), demonstrate that the minor groove oligo(A).oligo(T) constituents are not sufficient for high specificity DNA binding. These data constrain the possible models for Dat1p/oligo(A).oligo(T) complexes, suggest that the DNA binding domain is in an extended structure when complexed to its cognate DNA, and show that Dat1p binding sites are more prevalent than previously thought.