Divergent genes for translation inition factor elF-4A are coordinately expressed in tobacco

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Abstract
Three cDNA clones coding for eukaryotic translation initiation factor 4A, elF-4A, were isolated from a Nicotiana plumbaginifolia root cDNA library by heterologous screening. The clones comprise two distinct gene classes as two clones are highly similar while the third is divergent. The genes belong to a highly conserved gene family, the DEAD box supergene amily, although the divergent clone contains a DESD box rather than the characteristic DEAD box. The two clones are representatives of separate small ultigene families in both N. plumbaginifolia and N. tabacum. Representatives of each family are coordinately xpressed in all plant organs examined. The 47 kD polypeptide product of one clone, overexpressed in E. coli, crossreacts immunologically with a rabbit reticulocyte elF-4A polyclonal antibody. Taken together the data suggest that the two Nicotiana elF-4A genes encode translation initiation factors. The sequence divergence and the coordinate expression of the two Nicotiana elF-4A families provide an excellent system to determine if functionally distinct elF-4A polypeptides are required for translation initiation in plants.