Evidence of a codon restriction hypothesis of cellular differentiation: multiplicity of mammalian leucyl-sRNA-specific synthetases and tissue-specific deficiency in an alanyl-sRNA synthetase.

Certain suggested models of cell differentiation during ontogeny have important implications for cell and organismic senescence.Thus, as pointed out byWeismann,l and later by Minot,2 Pearl,3 and Mledawar,4 aging may be, in large measure, a