Soybean (Glycine max L.) Nuclear DNA Contains Four tufA Genes Coding for the Chloroplast-specific Translation Elongation Factor EF-Tu

Abstract

The chloroplast tufA gene codes for the translation elongation factor EF-Tu. In algae like e.g. Euglena tufA is part of the chloroplast DNA but in land plants the equivalent gene is transposed to the nuclear DNA. Using a previously sequenced Euglena gracilis tufA DNA probe a cDNA library from soybean was screened. Two cDNA clones (cDNA1 and cDNA2) were sequenced (ca. 500 nucleotides) and shown to contain parts of the chloroplast tufA gene. A cDNA1 fragment was used to screen a genomic library and one complete tufA gene was sequenced including 640 nucleotides of the region upstream of the transcription start site which was identified by S1 endonuclease protection experiments. The soybean genome contains four tufA genes which belong to two subfamilies with two members each. TufA mRNA is absent in dark grown seedlings but light grown seedlings contain a stable tufA mRNA of ca. 1.6 -1.7 kb. The open reading frame codes for a chloroplast transit peptide (71 amino acids) and a very conservative chloroplast EF-Tu protein.