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Cell fate specification in the CNS is controlled by the secreted morphogen sonic hedgehog (Shh). At spinal cord levels, Shh produced by both the notochord and floor plate (FP) diffuses dorsally to organize patterned gene expression in dividing neural and glial progenitors. Despite the fact that two discrete sources of Shh are involved in this process, the(More)
The symmetric pattern of codon degeneracies is discussed by using empirical arguments processed within a group-theoretic framework. It is reasoned that the genetic code is a relation rather than a mapping, and the symmetry of a relation defined on the codons is investigated. The principal results are (i) a new extraction of the basic symmetry inherent in(More)
Picosecond time-resolved fluorescence studies of 8-anilino-1-naphthalenesulfonic acid (A N S) have been carried out in a water-ethanol mixed-solvent system. Combined with quantum yield results, these data provide further insight into the nonradiative processes that can take place in this interesting fluorescence probe molecule. In a mixed solvent, the(More)