The nucleotide sequence of the DNA ligase gene (CDC9) from Saccharomyces cerevisiae: a gene which is cell-cycle regulated and induced in response to DNA damage.

The CDC9 gene of Saccharomyces cerevisiae encodes a DNA ligase, and we have determined the nucleotide sequence of a 3.85 kb fragment of DNA which encompasses the convergently transcribed CDC9 and CDC36 genes. S1 nuclease mapping has revealed a major 5' end for the CDC9 mRNA, and one major and one minor site for 3' polyadenylation. These two sites lie within the C-terminal coding region of the CDC36 gene, implying that these two genes are transcribed from overlapping sequences. An interesting structural feature of the CDC9 gene is a series of 6 hexanucleotide repeats (ATGATT) which occur within the 650 bp immediately upstream from the site of transcription initiation. These repeat elements may be implicated in the cell division cycle regulated expression of CDC9. Comparison of the predicted amino acid sequence of the yeast DNA ligase (Mr 84,806) with the sequences of the T4 and T7 bacteriophage DNA ligases reveals little similarity except for a stretch of approximately 45 amino acids, comprising 3 short homologous segments. This region may represent an ATP-binding domain common to polynucleotide ligases.