Thi1, a thiamine biosynthetic gene inArabidopsis thaliana, complements bacterial defects in DNA repair

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Abstract
AnArabidopsis thaliana cDNA was isolated by complementation of theEscherichia coli mutant strain BW535 (xth, nfo, nth), which is defective in DNA base excision repair pathways. This cDNA partially complements the methyl methane sulfonate (MMS) sensitive phenotype of BW535. It also partially corrects the UV-sensitive phenothpe ofE. coli AB1886 (uvrA) and restores its ability to reactivate UV-irradiated λ phage. It has an insert of ca. 1.3 kb with an open reading frame of 1047 bp (predicting a protein with a molecular mass of 36 kDa). This cDNA presents a high homology to a stress related gene from two species ofFusarium (sti35) and to genes whose products participate in the thiamine biosynthesis pathway,THI4, fromSaccharomyces cerevisiae andnmt2 fromSchizosaccharomyces pombe. TheArabidopsis predicted polypeptide has homology to several protein motifs: amino-terminal chloroplast transit peptide, dinucleotide binding site, DNA binding and bacterial DNA polymerases. The auxotrophy for thiamine in the yeastthi4::URA3 disruption strain is complemented by theArabidopsis gene. Thus, the cloned gene, namedthi1, is likely to function in the biosynthesis of thiamine in plants. The data presented in this work indicate thatthi1 may also be involved in DNA damage tolerance in plant cells.