MOLECULAR-CLONING OF A GENE REQUIRED FOR DNA-REPLICATION IN USTILAGO-MAYDIS

TSD2, a gene necessary for DNA synthesis in Ustilago maydis, was clone d by complementation of the temperature sensitive growth defect of a m utant known previously as poll-1 and renamed here tsd2-1. Linkage anal ysis established that the cloned fragment contained an allele of tsd2- 1 and not a suppressor. DNA sequence determination of the cloned DNA f ragment indicated the presence of a single large uninterrupted open re ading frame capable of encoding a protein of 845 amino acids without h omology to any known gene involved in DNA synthesis. TSD2 was found to be cell cycle-regulated and mRNA levels peaked in early S or G(1) pha se.