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STUDIES ON THE ROLES OF THE PROTEIN FACTORS CO-EIF-2 AND CO-EIF-2A('80) AND THE NUCLEOTIDE GDP IN THE REGULATION OF PROTEIN SYNTHESIS INITIATION IN RABBIT RETICULOCYTES
Abstract
A high molecular weight rabbit reticulocyte protein factor Co-eIF-2 regulates eIF-2 activity during initiation of protein synthesis. Co-eIF-2 contains Co-eIF-2A and Co-eIF-2C activities. Co-eIF-2A activity stimulates Met-tRNA(,f) binding to eIF-2 and stabilises the ternary complex, TC, Met-tRNA(,f).eIF-2.GTP. Co-eIF-2C activity stimulates Met-tRNA(,f) binding to eIF-2 in the presence of Mg('2+). Recently we have purified an 80 kd polypeptide Co-eIF-2A('80) possessing Co-eIF-2A activity and our results suggest that this protein is an integral component of Co-eIF-2 protein complex. Our studies on the roles of Co-eIF-2, Co-eIF-2A('80) and GDP in TC and Met-tRNA(,f).40S initiation complex formation indicate that: (i) Purified eIF-2 contains bound GDP. (ii) In the absence of Mg('2+), this eIF-2 bound GDP can be readily released and TC is formed. Both Co-eIF-2 and Co-eIF-2A('80) can stimulate this TC formation. (iii) In the presence of Mg('2+), eIF-2 apparently exists in an inactive conformation. GDP remains tightly bound to eIF-2 and TC formation is inhibited. Co-eIF-2 but not Co-eIF-2A('80) is effective in promoting GDP release from eIF-2 and the former is more effective in stimulating TC formation than the latter. We believe that Co-eIF-2 restores active conformation of eIF-2 which permits release of bound nucleotides from eIF-2 and facilitates TC and 40S initiation complex formation. (iv) When eIF-2 is phosphorylated by HRI and ATP, Co-eIF-2 is unable to displace GDP from eIF-2 (alpha) (P).GDP and TC formation is inhibited. In another study, we compared the characteristics of eIF-2 and eIF-2-ancillary factor activities from rabbit reticulocytes and brine shrimp Artemia Salina. Our results demonstrate that: (I) TC formed by Artemia eIF-2, is not inhibited by Mg('2+), (II) Artemia eIF-2 requires Mg('2+) for maximum GDP binding, and (III) Artemia eIF-2 and Artemia 40S ribosomes do not recognise reticulocyte Co-eIF-2C activity. These results suggest that regulatory mechanisms involving Mg('2+)-sensitive eIF-2 activity and high molecular weight Co-eIF-2 protein complex may not be operative in Artemia.
Subject Area
Biochemistry
Recommended Citation
BAGCHI, MILAN KUMAR, "STUDIES ON THE ROLES OF THE PROTEIN FACTORS CO-EIF-2 AND CO-EIF-2A('80) AND THE NUCLEOTIDE GDP IN THE REGULATION OF PROTEIN SYNTHESIS INITIATION IN RABBIT RETICULOCYTES" (1984). ETD collection for University of Nebraska-Lincoln. AAI8509855.
https://digitalcommons.unl.edu/dissertations/AAI8509855