Nuclear ribonucleoprotein complexes of amphibian liver. II. Changes in the protein moiety during development.

Ribonucleoprotein complexes composed of small molecular weight nuclear RNA (4--9 S) and proteins were isolated from hepatic nuclei of Rana catesbeiana (bullfrog) and the protein moiety of this nuclear ribonucleoprotein complex compared during different stages of development. SDS-polyacrylamide gel analysis of premetamorphic tadpoles and adult frog nuclear ribonucleoprotein complexes revealed that while the protein profiles of these two particles were very similar polypeptides of 47,000, 70,000, and 11,000 molecular weight were present in significantly higher concentrations in the frog ribonucleoprotein complexes. Comparison of the chromatin proteins isolated from these two developmental stages demonstrated that these three polypeptides of frog ribonucleoprotein were not contaminants from chromatin. Since these three polypeptides could not be preferentially extracted from the frog ribonucleoprotein complex by 0.5 M KCl or 1 M urea, it was unlikely that these polypeptides were bound nonspecifically to the ribonucleoprotein particle. Polypeptide analysis of the nuclear ribonucleoprotein complexes isolated from tadpoles immersed in the thyroid hormone L-thyroxine revealed an increase in two polypeptides of 37,000 and 45,000 molecular weight during metamorphosis. The absence of reduced amount of these two polypeptides in either the premetamorphic tadpole or adult frog demonstrated that their presence in Rana catesbeiana nuclear ribonucleoprotein was transient during development and specifically associated with tadpole metamorphosis. We conclude from these experiments that the nuclear ribonucleoprotein complex is a dynamic structure during Rana catesbeiana development and that specific changes in its protein composition are associated with discrete stages of amphibian development.