CDC54 BELONGS TO THE CDC46 MCM3 FAMILY OF PROTEINS WHICH ARE ESSENTIAL FOR INITIATION OF EUKARYOTIC DNA-REPLICATION/

CDC54 is a gene essential for initiation of DNA replication in Sacchar omyces cerevisiae, and which is known to genetically interact with oth er regulators of the S-phase, including CDC46. We describe the isolati on and sequencing of CDC54 and show that it encodes a protein structur ally related to Cdc46p, Mcm2p and Mcm3p by the presence of a conserved domain of 145 amino acids which is internal to each polypeptide. This conserved domain resembles the DEAD box of RNA helicases and is simil ar to the conserved domain associated with a group of transcription an d replication factors with known or assumed DNA-dependent ATPase activ ity, suggesting it may be involved in nucleic-acid recognition. Compar ison of Cdc54p to related proteins from other species revealed that it closely resembles cdc21p from Schizosaccharomyces pombe.