TABLE 2.

SIR2 alleles

SIR2 allele	Amino acid changes
sir2-604	D515Y Δ30C
sir2-614	E174G N299I L438H K523E K542R
sir2-620	S204P K414R K475E V500A Δ24C

A shorthand description for mutations present in each allele is used. For amino acid substitutions, the wild-type amino acid (in its one-letter code) and position are listed, followed by the amino acid replacing it in the mutated allele. For deletions caused by premature stop codons, the number of amino acids removed is listed after the “Δ,” followed by a “C” for carboxy-terminal deletion. Amino acid changes known to be sufficient to confer the temperature-sensitive mating phenotype are in italics (M. Hickman and S. Holmes, unpublished results). Both N299I and L438H mutations of sir2-614 are necessary to observe the temperature-sensitive phenotype. SIR2 alleles containing only the Δ24C, K475E, or K414R/K475E mutations found in sir2-620 exhibit no mating phenotypes.