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During the cloning of a genomic DNA encoding mitochondrial thioredoxin (TRX) from the fission yeast Schizosaccharomyces pombe, its 5′ flanking sequence was involved in the high-frequency of transformation. The recombinant plasmid pYEX that was constructed in the 2 μ plasmid-derived vector pYES2 gave rise to a significant high-frequency of transformation in S. pombe, compared to the vector alone. Plasmid pYEX contains 1,090 bp 5′-flanking sequences of the TRX gene that are ahead of the open-reading frame. Similar 5′-flanking sequences, which were inserted in the lacZ fusion vector YEp357R that contained the 2 μ origin of replication, also gave a high-frequency of transformation. Dissection of the 5′-flanking sequence of the TRX gene by the HindIII restriction site showed that the 782 bp flanking sequence (5′ upstream of the HindIII site) was responsible for the high-frequency of transformation by the 2 μ plasmid-derived vector DNAs. The putative sequence that is involved in the highfrequency of transformation contains a very high ratio of A-T pairs. No known functions were assigned on the sequence, which was estimated from the GenBank database.


During the cloning of a genomic DNA encoding mitochondrial thioredoxin (TRX) from the fission yeast Schizosaccharomyces pombe, its 5′ flanking sequence was involved in the high-frequency of transformation. The recombinant plasmid pYEX that was constructed in the 2 μ plasmid-derived vector pYES2 gave rise to a significant high-frequency of transformation in S. pombe, compared to the vector alone. Plasmid pYEX contains 1,090 bp 5′-flanking sequences of the TRX gene that are ahead of the open-reading frame. Similar 5′-flanking sequences, which were inserted in the lacZ fusion vector YEp357R that contained the 2 μ origin of replication, also gave a high-frequency of transformation. Dissection of the 5′-flanking sequence of the TRX gene by the HindIII restriction site showed that the 782 bp flanking sequence (5′ upstream of the HindIII site) was responsible for the high-frequency of transformation by the 2 μ plasmid-derived vector DNAs. The putative sequence that is involved in the highfrequency of transformation contains a very high ratio of A-T pairs. No known functions were assigned on the sequence, which was estimated from the GenBank database.