A truncated Sir4C is sufficient for silencing at <i>HML</i> and <i>HMR</i>.

<p>A) Scheme of Sir4 indicating important domains and their interactions. The N-terminal domain of Sir4 (Sir4N) is in red, the C-terminal domains in green (full Sir4C = 747–1358; light green PAD = 950–1262; dark green coiled coil domain = 1262–1358). B) Scheme of plasmids expressing Sir4 constructs. The plasmid's original promoter and terminator were replaced with a 1 kb sequence of the <i>SIR4</i> 5′ region and 250 bp of the 3′ region containing the endogenous promoter/terminator information. The same plasmid construct with different markers was used as needed. C) Silencing at <i>HML</i> of strains with various Sir4 domains was assayed by quantitative mating to a tester strain (GA858). The endogenous <i>SIR4</i> copy was full length (<i>SIR4</i>; GA503), a C-terminal deletion (<i>sir4N</i>; GA5809) or a complete deletion of Sir4 (<i>sir4</i>Δ; GA5822). C-terminal or full length Sir4 was added back on a plasmid. Mating efficiency was normalized to the wild-type strain; data represent mean value ± s.e.m, n.d. undetermined values. D) Plasmids similar to (C), but silencing at <i>HMR</i> was assayed using a <i>TRP1</i> reporter (GA484, GA6072, GA5886). Serial dilutions of transformed strains were grown on control plates selecting for the plasmid only or on plates selecting for the plasmid and growth without tryptophan (monitoring repression of <i>TRP1</i>).