THE ELONGATION-FACTOR-1 A-2 ISOFORM FROM RABBIT - CLONING OF THE CDNAAND CHARACTERIZATION OF THE PROTEIN

Eukaryotic elongation factor 1 A (eEF1A, formerly elongation factor-1 alpha) is an important component of the protein synthesis apparatus. H ere we report the isolation and characterization of the cDNA sequence encoding rabbit eEF1A-2, an isoform of eEF1A, as well as a structural and functional comparison of the two rabbit isoforms, Northern analysi s of the expression pattern of eEF1A-2 showed that this isoform is exp ressed in skeletal muscle, heart, brain and aorta, while transcripts a re not detected in liver, kidney, spleen and lung. In contrast, the pr eviously characterized eEF1A-1 isoform is expressed in all tissues exa mined except skeletal muscle. We have recently purified eEF1A-2 from r abbit skeletal muscle. By partial amino acid sequencing and determinat ion of the posttranslational modifications of eEF1A-2 we found that bo th of the glycerylphosphorylethanolamine modifications observed in eEF 1A-1 appear to be present in eEF1A-2, However, two of the residues fou nd dimethylated in eEF1A-1 appeared to be trimethylated in eEF1A-2, A comparison of the enzymatic activity showed that eEF1A-1 and eEF1A-2 h ave indistinguishable activity in an in vitro translation system. In c ontrast, the GDP dissociation rate constant is similar to 7 times high er for eEF1A-1 than for eEF1A-2, The nucleotide preference ratio (GDP/ GTP) for eEF1A-1 was 0.82, while the preference ratio for eEF1A-2 was 1.50.