A POLLEN-SPECIFIC DEAD-BOX PROTEIN RELATED TO TRANSLATION INITIATION-FACTOR EIF-4A FROM TOBACCO

A pollen-specific sequence, NeIF-4A8, has been isolated from a cDNA library from mature pollen of Nicotiana tabacum cv. Samsun. NeIF-4A8 is a full-length cDNA whose deduced amino acid sequence exhibits high homology to the eucaryotic translation initiation factor eIF-4A from mouse, Drosophila and tobacco. eIF-4A is an RNA helicase which belongs to the supergene family of DEAD-box proteins. Northern blot analysis with a gene-specific probe showed strict anther-specific expression of NeIF-4A8 starting at microspore mitosis. With antibodies raised against tobacco eIF-4A the presence of abundant eIF-4A-related proteins in developing anthers and pollen grains was demonstrated. The genomic analysis shows that the coding region is split by three introns whereas a large, fourth intron is situated in the 5'-untranslated region. A promoter construct with 2137 bp of upstream sequence fused to the GUS reporter gene was used to confirm that the expression is confined to the haploid cells within the anther. NeIF-4A8 is a prime candidate for mediating translational control in the developing male gametophyte.