Regulation of catabolism of microinjected ribonuclease A requires the amino-terminal 20 amino acids.
RNase A introduced into the cytoplasm of IMR-90 human diploid fibroblasts by erythrocyte-mediated microinjection is degraded with a half-life of approximately equal to 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.
D000595:Amino Acid Sequence; D002459:Cell Fusion; D002478:Cells, Cultured; D004912:Erythrocytes / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008845:Microinjections; D010446:Peptide Fragments / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism*; D013329:Structure-Activity Relationship
D010446:Peptide Fragments; D012260:Ribonucleases