Molecular characterisation of the DNA ligase gene, CDC17, from the fission yeast Schizosaccharomyces pombe.

We have sequenced a 4200-base-pair fragment of Schizosaccharomyces pombe DNA which encompasses the entire DNA ligase gene, CDC17. S1 mapping has enabled us to identify two small introns (40 and 62 nucleotides) at the 5' end of the coding region of the gene and their 3' internal conserved sequences match the CTRAY consensus found in other S. pombe introns. The major transcription initiation and 3' polyadenylation sites have been mapped and are preceded by higher eukaryotic-like TATA and AATAAA sequences respectively. Furthermore, the CDC17 mRNA carries a poly(A) tail whose length (approximately 250 nucleotides) is typical of that found in higher eukaryotic mRNAs, and is in contrast to the much shorter polyadenylated sequences found for the mRNAs of the budding yeast, Saccharomyces cerevisiae. The deduced amino acid sequence of the S. pombe DNA ligase predicts a protein of 86182 daltons, and an overall 53% homology with the same enzyme from S. cerevisiae. In particular, a stretch of 24 amino acids with 100% sequence homology spans the putative ATP-binding region which is also conserved in T4 and T7 bacteriophage DNA ligases.