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Nucleic Acids Research, 1994, Vol. 22, No. 18 3773-3778
© 1994

MOLECULAR BIOLOGY

The topoisomerase I gene from Ustilago maydis: sequence, disruption and mutant phenotype

David Gerhold, Manimekalai Thiyagarajan and Eric B. Kmiec*

Department of Pharmacology, Jefferson Cancer Institute, Thomas Jefferson University 233 S. 10th Street, Philadelphia, PA 19107, USA

*To whom correspondence should be addressed

Received May 3, 1994. Revised July 26, 1994. Accepted July 26, 1994.

The Ustilago maydis genomic TOP1 gene encoding DNA topoisomerase I was cloned by amplifying a gene fragment using the polymerase chain reaction, and using this fragment to search a genomic DNA library by hybridization. The predicted peptide sequence exhibited 30–40% identity to other eukaryotic TOP1 genes, yet differed in several features. First, an unusually long acidic region was identified near the amino terminus (28/29 residues are acidic), which resembles other nucleolar peptide motifs. Second, an atypical carboxy-terminal 'tail', absent in other TOP1 genes, followed the active site tyrosine residue. A top1 gene disruption mutant was constructed by replacing the genomic TOP1 gene, with a top1::HygR null allele. This mutant lost the abundant topoisomerase I activity evident in wild-type U.maydis, and displayed a subtle coloration phenotype evident during cell senescence.


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