J. Biol. Chem., Vol. 255, Issue 15, 7055-7058, Aug, 1980
A cytoplasmic ribonucleoprotein complex containing a small RNA inhibitor of protein synthesis
J Bag, M Hubley and B Sells
Ribonucleoprotein complexes (RNP) sedimenting between 10 and 15 S were
isolated from the postpolysomal cytoplasmic fraction of embryonic chicken
muscle. These RNP complexes lack mRNA but contain RNA with a sedimentation
coefficient of 4.4 S. The 4.4 S RNA did not arise as a product of
degradation during the course of the isolation procedure nor did it contain
oligo(U)- or poly(A)-rich regions. Furthermore, the 4.4 S RNA-containing
RNP complex was easily separable from free mRNPs and, therefore, is not
considered as part of the free mRNP complexes. Both the 4.4 S RNA and 10 to
15 S RNP were able to inhibit translation of either "capped" or "uncapped"
mRNA in a heterologous cell-free system. This inhibitory effect may result
from interference of 4.4 S RNA with an early event in mRNA translation. A
large number of polypeptides of Mr = 14,000 to 220,000 were present in the
10 to 15 S RNP. Among these, the most prominent polypeptides were of Mr =
36,000; 48,000; 52,000; 58,000; 65,000; 78,000; 84,000; 96,000; 105,000;
165,000; and 220,000. With the exception of the Mr = 36,000 polypeptide,
these major components were also found in the nonpolysomal cytoplasmic mRNA
protein complexes (free mRNP).
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