Cell elongation definition

Auxins are defined as organic substances that promote cell elongation when applied in low concentrations to plant tissue segments in a bioassay. By this definition, there are several other native auxins that have been reported to occur in plants in addition to the most often studied auxin, IAA. These include the halogen-substituted 4-C1-IAA,23 as well as phenylacetic acid and indole-3-butyric acid.24 All native auxins are found in planta as both free acids and conjugated forms through ester or amide linkages. IAA, the auxin most extensively studied, will be the focus of this chapter. 

Fig. 9. Comparison of amino acid sequences of bovine mouse rat a, a (partial), retinal rod and cone cells < bacterial elongation factor EFTu and c-Ha-ras, aligned to maximize matching. This leads to the definition of an aavp of 3% amino acids (numbers above sequences). Boxes surround identical or conserved residues, (c) and (p), residues ADP-ribosylated by CTX and PTX, respectively. —A—, — C—, —E— and —G—, sequences known to be intimately involved in guanine nucleotide binding by EFTu (From Refs. 175 and 176).

Initiation of protein synthesis in mammalian cells proceeds by a complex process whereby the assembly of mRNA, the ribosome, and initiator met-tRNAf into an initiation complex is catalyzed by a group of proteins called initiation factors. By definition, these proteins are not required for polypeptide chain elongation. A detailed discussion of this process, and the role of individual initiation factors can be found in this volume (Kaempfer, 1984), or in other recent reviews (Benne and Hershey, 1978 Jagus et al., 1981) which also contain pertinent references. Nine initiation factors have been highly purified from rabbit reticulocytes, and still other factors have been described which may serve auxiliary functions, or indeed may qualify as initiation factors in their own right. A very brief (and oversimplifed) description of the role of the nine, characterized initiation factors is listed below, along with the step in initiation complex formation in which each participates ... 

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