RNase A introduced into the cytoplasm of IMR-90 human diploid fibroblasts by erythrocyte-mediated microinjection is degraded with a half-life of ~75 hr in the presence of fetal bovine serum. In response to serum deprivation the degradative rate of microinjected RNase A is enhanced 2-fold. RNase S protein (amino acids 21-124) is degraded with a half-life similar to that of RNase A in the presence of serum, but its catabolism is not increased during serum withdrawal. Reconstitution of RNase S protein with RNase S peptide (amino acids 1-20) restored full enzymatic activity to the S protein as well as the ability of fibroblasts to increase its catabolism during serum deprivation. Finally, RNase S peptide microinjected alone shows the full 2-fold increase in degradative rate during serum withdrawal. These results show that recognition of RNase A for enhanced breakdown during serum deprivation is based on some feature of its amino-terminal 20 amino acids. Furthermore, our results indicate that the enhanced protein catabolism during serum deprivation can be highly selective.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Issue number||8 I|
|State||Published - 1983|
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