Control of Protein Synthesis in Acanthamoeba castellanii

Abstract

During development of Acanthamoeba castellanii in a non‐nutrient medium, the pattern of synthesis of proteins changes. Comparison of in vivo and in vitro patterns of protein synthesis reveals concomitant relative increases of five proteins, indicating a control of synthesis of these proteins at the level of the RNA content. The decrease in the overall rate of protein synthesis and relative decreases in the synthesis of actin and ribosomal proteins during development, not accompanied by equivalent changes in the content of mRNA, suggest control mechanisms also at the level of translation. Patterns of ribosomal proteins do not change qualitatively during encystation, indicating that the inhibition in the overall rate of protein synthesis and the formation of inactive monosomes is not controlled by this mechanism; however, phosphorylation of one ribosomal protein, S 3, is observed occasionally during encystation. Phosphorylation of S 3 is also detected after transfer of stationary phase cells into fresh nutrient medium. It was found that only such cells having RNA of aberrant properties are able to phosphorylate S 3 after transfer into fresh nutrient medium. Since these changes in the property of RNA are never observed in cysts, in which phosphorylation of S 3 sometimes occurs, it is concluded that either other alterations in the properties of RNA than those detected or other parameters are responsible for changes in phosphorylation of S 3.

Effect of essential amino acids on the phosphorylation of a 40S ribosomal protein and protein synthesis in Acanthamoeba castellanii

“…Phosphorylation of ribosomal protein versus growth status and growth condition Earlier studies revealed the phosphorylation of one basic 40s ribosomal protein 53 in Acanthamoeba (Jantzen, 1981a;Jantzen et al, 1983). Figure 1A Role of essential amino acids in S3 phosphorylation Earlier results have indicated that amino acids arginine, methionine, leucine, isoleucine, and valine are essential in Acanthamoeba (Dolphin, 1976).…”

“…Withdrawal of the nonessential amino acid histidine does not influence the growth rate and the S3 phosphorylation pattern. Control experiments show that low levels of phosphorylated S3 in response to amino acid deficiency, are not simply the consequence of cessation of growth, since growth arrested KHzPOcdepleted and encysting cells (Jantzen et al, 1983) contain phosphorylated S3 derivatives. After supplementation of amino acid-deficient media, a dose-dependent induction of S3 phosphorylation occurs, leading transiently to the most highly phosphorylated forms of S3.…”

“…This is shown by the fact that transfer of stationary phase ND cells into fresh nutrient medium, transiently induces S3 phosphorylation leading to the most highly phosphorylated forms of S3. Another example is the induction of S3 phosphorylation after transfer of ND cells into non-nutrient encystment medium (Jantzen et al, 1983). One possible hypothesis which could explain different levels or 53 phosphorylation in log phase D and ND cells as well as transient high S3 phosphorylation levels after transfer of ND cells into non-nutrient encystment medium is that S3 phosphorylation is effected by different biochemical pathways.…”

“…In exponentially growing Tetrahymena (Cuny et al, 1985), Dictyostelium (Juliani et al, 19831, and Acanthamoeba (Jantzen, 1981a;Jantzen et al, 1983) phosphorylation of ribosomal protein is not observed, while transfer of these cells to nutrient-depleted media leads to effective phosphorylation of a 40s ribosomal protein. The results shown here support our earlier finding that log phase cells of Acanthamoeba, cultivated in a nondefined nutrient medium (ND cells), contain low levels of the phosphorylated 40s ribosomal protein S3.…”