Complementation of rid mutants with cloned DNA fragments. (A) Wildtype or rid1-1 cells were transformed with plasmid DNA containing the orc1+gene or no orc1+(empty). Only those cells transformed with orc1+containing DNA were capable of growing at the restrictive temperature of 36°C. (B) Wildtype or rid2-1 cells were transformed with plasmid DNA containing mcm4+or no mcm4+(empty). Only cells transformed with mcm4+DNA were capable of growing at 36°C. (C) Schematic diagram of rid1-1 showing the position of the mutation in the C-terminal portion of Orc1. (D) Schematic diagram of rid2-1 showing the position of the mutation in Mcm4 signature motif III, relative to the Walker A and Walker B binding motifs. The number 509 corresponds to the first amino acid position for motif III. The Mcm4 signature motifs are 10-12 amino acids long. (E) Sequence comparison of motif III from various organisms including human indicating strong evolutionary conservation for this region of the protein. The position of the rid2-1 mutation is shown.